with 10-13 cubes you could do 3 15s no probs. but try to lean closer to 12 so each get 4 at least depending on sub that should be good
box is 12.7 before displacement and i was considering the RE-SXX but the 15's require 4cu so after displacement idk how good it would sound
so i guess the new question is 3 15's or 5 12's