You might want to consider a diagonal set up with the spearkers on each side of the corner if you want to use the 15x15 room. I have a basically square 17x17 room and I use this set up. It sounds pretty good with no acoustic treatment, although I plan on doing more with that at some point. I had a more common set up with the speakers on one wall, and I had a lot more problems. WIth the diagonal set up the sound is very good in my listening position with no trreatment (but watch out if you go into the corners when the bass is cranked up!).
I know a lot of speaker manufacturers such as Bobby at Merlin uses this set up for shows when they have a small square room. I think I'd get further benefit from bass traps and some acoustic panels at least for primary reflection points.
I know a lot of speaker manufacturers such as Bobby at Merlin uses this set up for shows when they have a small square room. I think I'd get further benefit from bass traps and some acoustic panels at least for primary reflection points.