My wife and I own Delta 12.10's and we recently had the opportunity to try out 5 other boats from the Delta fleet, including the 2017 Delta 15s. My wife is 5'6" - 125lbs and I am 5'11" - 170lbs (33" waist).
The 15s was easily BOTH of our favorites - hands down. The "S" suffix indicates a smaller cockpit size and we both found it offered a superior fit. It felt like we were one with the craft and didn't feel cramped in the least. It made getting back into the "non-S" models feel like a pair of pants that were way too big. In the non-S models, my legs felt like they had to frog-leg out to brace the hull. The 15s is narrow and tighter and fits like a glove.
My wife and I are both looking at upgrading from the 12.10 so we can go on some longer, multi-day trips. At first I didn't even consider the 15s and didn't even want to try it, but I'm sure glad I did.
We'll be picking up a pair of these in the next few weeks.