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Also in this series: 16-20, 21-25, 26-30, 31-35, 36-40.

15. Travis Harrison | Third Base | DOB: 10/92 | Bats: Right | Draft: 2011-1

YEAR     LV      PA      AVG      OBP      SLG     HR    XBH     BB     SO
2012     RK+    253     .301     .383     .461      5     21     24     51
2013     A-     537     .253     .366     .416     15     43     68    125

Travis Harrison was selected by the Twins with the 50th pick in the 2011 draft as compensation for losing Orlando Hudson as a free agent and signed away from USC for $1.05 million. Touted as one of the best bats in the high school class, Harrison had an impressive debut at rookie-ball and then showed some of his flaws last year while moving up to full-season competition, hitting just .253 while striking out 125 times in 129 games.

Combined with his rookie-ball showing Harrison has 176 strikeouts in 189 games, which is a red flag in the low minors. Beyond that his power has been somewhat underwhelming after being billed as elite coming out of high school, with 20 homers and a .161 Isolated Power in 790 total plate appearances. That's certainly not a lack of power, especially considering Harrison played last season at age 20, but given questions about his ability to stick at third base he needs to mash.

One bright spot is that Harrison drew 68 walks last season and also got plunked by 14 pitches, which suggest he should be able to get on base at a decent clip even if all the strikeouts keep his batting average modest. Ultimately much of his value depends on where he ends up defensively and how much power he can develop by the time he reaches Minnesota. So far he's shown enough to be an intriguing prospect, but the edges are still pretty rough.

14. Danny Santana | Shortstop | DOB: 11/90 | Bats: Switch | Sign: Dominican

YEAR     LV      PA      AVG      OBP      SLG     HR    XBH     BB     SO
2011     A-     409     .247     .298     .373      7     27     25     98
2012     A+     547     .286     .329     .410      8     38     29     77
2013     AA     587     .297     .333     .386      2     34     24     94

Danny Santana is generally more highly thought of as a prospect than his performance in the minors would suggest based on the idea that athleticism, speed, and defense will eventually allow him to become a starting-caliber shortstop in the majors. At age 23 he still has an opportunity to develop further, but in the meantime he hasn't been all that impressive, making a lot of errors (for whatever that's worth) along with little power and awful strike zone control.

Last season he hit .297 at Double-A, but managed just two homers and 24 walks in 131 games on the way to a modest .333 on-base percentage and .386 slugging percentage. His numbers at high Single-A in 2012 were similar and combined during the past two seasons he totaled 10 homers in 1,134 plate appearances, struck out 171 times versus 53 walks, and was successful on just 66 percent of his steal attempts. Right now he projects as a sub par offensive player.

The good news is that Santana is still pretty young and the bar for offense at shortstop is very low, so even hitting, say, .275 with minimal power and a poor walk rate would make him a solid all-around player if his glove is a huge asset. If instead his defense at shortstop is merely decent, then his current offensive skill set leaves Santana looking like something less than a building block, even considering the Twins' longstanding inability to develop competent middle infielders.

13. Max Kepler | First Base | DOB: 2/93 | Bats: Left | Sign: Germany

YEAR     LV      PA      AVG      OBP      SLG     HR    XBH     BB     SO
2011     RK+    221     .262     .347     .366      1     15     23     54
2012     RK+    269     .297     .387     .539     10     31     27     33
2013     A-     263     .237     .312     .424      9     23     24     43

When the Twins signed Max Kepler out of Germany for $800,000 in 2009 he oozed potential. At age 16 he was still growing into a 6-foot-4 frame and had uncommon athleticism along with the unique background of parents who met while performing in the ballet. He was seen as a potential center fielder long term and performed well in the low minors, but Kepler took a step backward last season and has lost a lot of upside as he's matured physically.

He played primarily first base at low Single-A last season, in part because of an elbow injury that delayed this 2013 debut and in part because he no longer has the speed to handle center field on a regular basis. Going from center field to first base or an outfield corner puts far more pressure on the development of Kepler's bat and he hit .237 with a high strikeout rate last year. However, he also showed solid power and patience with nine homers and 24 walks in 61 games.

Kepler is still just 21 years old and still has considerable potential, but his upside has shrunk dramatically. At this point he needs to stay healthy and put up some big numbers offensively to re-emerge as a top prospect, as he's yet to play more than 61 games in a season and yet to advance past low Single-A. If the power arrives Kepler could reach Double-A this year and work his way into the Twins' plans for 2015, but for now he's a question mark.

12. Michael Tonkin | Reliever | DOB: 11/89 | Throws: Right | Draft: 2008-30

YEAR     LV      G     GS      ERA        IP       H     HR      SO     BB
2011     A-     48      3     3.87      76.2      82      3      69     24
2012     A-     22      0     1.38      39.0      29      1      53      9
         A+     22      0     2.97      30.1      24      2      44     11
2013     AA     22      0     2.22      24.1      21      0      30      8
         AAA    30      0     4.41      32.2      33      3      36      8
         MLB     9      0     0.79      11.1       9      0      10      3

Michael Tonkin was a 30th-round pick out of high school in 2008 and looked like a mediocre starter prospect in the low minors, but Jason Kubel's brother-in-law has emerged as a potential impact arm since switching to the bullpen full time in 2011. Tonkin stands 6-foot-7 with a mid-90s fastball and has racked up 242 strikeouts in 213 innings during the past three seasons, including an impressive nine-appearance debut with the Twins.

And unlike a lot of hard-throwing young arms Tonkin has also shown good control with a career walk rate of 2.4 per nine innings and just 19 walks in 68 innings last season while rising from Double-A to the majors as a 23-year-old. He's huge, he throws a very hard fastball-slider combo, he misses lots of bats, and he actually knows where the ball is going most of the time, which is the most reliable recipe for a good relief prospect.

Bullpen depth is one of the Twins' few strengths at this point, making it unclear how early Tonkin could be in the big-league relief mix this season, but he certainly looks MLB-ready and projects as a potential late-inning setup man for Glen Perkins. As a reliever in a stacked farm system Tonkin is often overlooked, but in terms of the ability to make an immediate impact few Twins prospects are better.

11. Lewis Thorpe | Starter | DOB: 12/95 | Throws: Left | Sign: Australia

YEAR     LV      G     GS      ERA        IP       H     HR      SO     BB
2013     RK-    12      8     2.05      44.0      32      2      64      6

Investing baseball's most resources into scouting Australia has yet to pay huge dividends for the Twins, producing a handful of marginal big leaguers and Grant Balfour, who starred elsewhere. Lewis Thorpe has a chance to change that after signing for $500,000 as a 16-year-old in 2012 and dominating rookie-ball in his pro debut last season, posting a 2.05 ERA and 64/6 K/BB ratio in 44 innings against Gulf Coast League hitters.

At age 18 he works in the low-90s and tops out in the mid-90s, complementing his fastball with a changeup that draws praise, and the extent to which he sliced up opponents last season suggests he's ready to skip a level of rookie-ball and go directly to low Single-A. Thorpe is the youngest of my top 20 prospects and if you want to feel really old consider that he was born six months after the Twins drafted Doug Mientkiewicz, so he's a long way from the big leagues.

In terms of long-term upside, however, few prospects in the Twins' farm system can compete with the 6-foot-2 left-hander and he has more polish than most rookie-ball pitchers. His place on this list reflects how I'm generally conservative when it comes to rankings prospects--and particularly pitchers--who've yet to face full-season competition, but Thorpe has cracked some prominent MLB-wide top-100 lists.