if your right handed, the peq-16 goes on the right rail, I usually put my laser even with the forward most rail. we also use vicker tactical (blueforce gear) 2 point slings.
I don't remember what adapter we use, but its just some low bid rail adapter.
we use the 15 also, it's just not as common. I just took a quick look at the photo and it looked like a 16 to me. same thing applies though. dominant side rail.