yes!!! haha
ok dude...
If you can fit 7 cubes in there, deffinately get one 18 over a 15, the efficiency and overall cone area will make a s***load difference with most subs.
I say either 3 12's, or if I were you I would deffinately get one dc level 4xl 18" or one level 5 18". Or if you can get your hands on one.... an lms hahaha (sorry I just sold mine

)
One very efficient and very powerful 18 is the way to go. With a level 5 you would be in the 50's...
and go with 6.5ish^3 with a huge port like 6" or so tuned to maybe 31hz.
You would push some crazy air.