I had the same issue and actually have about the same size wrist as you. 13.5 on a good day but when my wrist swelled in the summer or after workouts my bracelet drove me nuts. I had mine for a year before giving in and selling it and getting the 16. It’s a tiny bit big on me but I LOVE it now. Especially for the summer, it’s just so much more comfortable. I do agree with everyone who says it depends on your personal preference on how you want it to fit, and I thought I preferred a more snug fit, but the 15 was uncomfortably tight for me for half the year (I live in a climate that’s warm for half the year). I also didn’t feel it was very flattering on me because of how high up close to my hand it sat. My advice after going through my year-long ordeal is that if you have ANY doubts at all, at least try and see if you can still exchange it while you’re still within the exchange period. (Or at least give the 16 a second shot to be sure you made the right choice with your 15.) Otherwise you’ll always be wondering “what if?” I certainly drove my dear husband nuts by how often I asked him.
. Most days I feel I have the correct size, other days I think I should have gotten a different size 
