Will Revel Studio2s fit in a 15'x18'x9' room?

I have heard these speakers at a dealer in a smaller room which I guess would be about that size, and they sounded great, with little room effects. I would suggest powerful amps to control bass well and cables which do not enhance the bottom end. Every room is different so do a home trial to eliminate risk, if possible.

I have the Salon 2s in a 28X16 room with a 15' vaulted ceiling and they perform very well in that space, so I'd imagine the Studio 2s would work well in yours.

Any smaller and I would say no, but you just might squeeze them in. You may have too much bass, and will need to treat it either with processing or extensive passive treatments.

I have Studio 1s on the long wall, 13 x 20 or so, and I need to EQ the bass WAY down.

Treat the room with bass traps and you will be fine.