I can tell you from my experience in hearing a wide variety of speakers that the Maggies represent exactly what they are noted for-a wide soundstage, very low distortion (if any) and a realistic presentation of all instruments in their respective dynamic range.
Not only that, the vocal tracks, especially those of female singers seem to be as if they are right in the room with you! With regards to the size of the speakers from Magnepan. The larger models do have extended bass frequencies, such as the 3.7i and 20.7
However, the .7 or 1.7i would be best served in utilizing a subwoofer as well. I have the venerable and highly proclaimed 1.6 QR's. I am using a subwoofer with them of course. I am driving them with Quicksilver V4 Monoblocks! My room is 12x15 too!
It is quite loud with enough power and perfectly mated for these speakers! I agree that if you have a very large listening room that you might need a more powerful amplifier or maybe solid-state to drive the Maggies to reasonable levels, but once again that's an opinion!