15s can be absolutely violent depending on what you listen to. I've heard them in numerous configurations and have never been disappointed. I have a friend with 2 of them ported on huge power....it's ridiculous. I had a single 15 in 2.5 cubes ported on a shade under 2k and it shook my lowly Sonata to the bracing.
I'm curious about how the 12s will do personally.
What music will you be testing them with?