Why is my system so loud?

i have a pre-fab memphis car audio slot ported enclosure that came with my svc 15" M1 and after that piece of **** fried (first day i got it)... i put a normal piece of mdf over the opening and cut a 12" hole in it because i had an old piece of crap infinity kappa 12.1 layin around....i threw that in there and wired it up on my zx 1000.1 @ 4 ohm and its 10 times louder and 1000 times lower than the 15..... my buddy had the same situation when he blew his orion h2 i did the same thing but we put a 10" infinityreference in a 12" box and it was louder than the h2....so when my 15 gets back im just gunna sell it or trade it for a nasty 12 to put in the 15 box its soooo much louder you have no idea