After seeing Colin's response and considering how close the sim results were, I decided that I may not have run enough iterations for the sims. I re-ran the sims for approximately 1.5 billion iterations this time. The results did change, and Wong is correct, but the decision is still very close.
If your opponent is a basic strategy player, then you should stand on your 15 for a 74.49% chance of advancing vs 74.46% for hitting and 30.48% for doubling.
If your opponent will respond optimally, then you should hit to 17 for a 65.21% chance of advancing vs 64.60% for standing and 30.26 for doubling.
Sorry for any confusion. I'll try not to be so eager that I post incomplete results next time.