Mine had 16" wheels and I have a set of 15" wheels on it now with my 31" KM2's and it's perfectly fine. I wish I could have got more of an offset rim, but it's fine. 3.5" of offset is as close as you want to get, my caliper is mighty tight with the rim. All things considered, you don't need so much meat on those calipers. I took a grinder to my calipers JIC and ground down some of the pointless bulbous sections that were closest to the rim. PERFECTO!
I have no problems with them. Just got to make sure you don't have the big brake type deal that my buddy had on his, but he had to use 17" wheels. 16" wheels were merely an option from the factory, so 15's with enough offset will do you good.
1996 Toyota Tacoma 3RZ, 5 speed
K&N drop in, ToyTec 3" front spring spacers, 3" AALs, Rancho rear shocks, Flowmaster exhuast, Cat delete, D&S front rotors, BFG KM2s 31x10.5x15