You should take a look at the ssa zcon 15, all of ssa's products are designed with sq in mind but they still get pretty darn loud. A d2 would be perfect for your amp and you would actually save a little bt of space by going with 1 15 over 2 12s. Tune your box to 28-30hz and you should be pretty happy.
I just came from 2 12 AQ hdc3 to 1 15 custom and I might of lost a db on the tl but to the ear I doubt u can tell a difference buy it sounds much cleaner. Watts are over rated sounding good is what matters
You will lose a lot of output if those 15s were in a proper box but they were only type r (I think u said) I ran 2500 off 2 12 and get the same 2500 off 1 15 and it sounds the same and I have a way lower tuning.