All of the already releases mobile CPUs are in the 15W class, so yes, they are absolutely suitable for the nTB 13" MBP. If Intel decides not to release 15W chips with Iris graphics, these would be the chips Apple had to go with if they don't want to give the nTB MBP the same 28W chips they use in the TB MBP and if they won't go with AMD. Now, it might be possible Intel releases 15W CPUs with Iris graphics, but looking at the thermal data from the notebooks already released, Intel might have a hard time giving more wattage to the iGPU in these chips without having the CPU thermal throttling too fast.
Having said that, Apple might not have a problem with building a lower end iGPU in the nTB MBP. After all, they see this notebook as the MacBook Air replacement, and differentiating it a little more to the more expensive Touch Bar model is something most business people would love to do.