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

Are they too much speaker to perform well?
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.
I would go for it. The room's not THAT small, and you can trim the speaker's bass characteristics with the rear mounted controls which actually work very well. Good luck
I own Studio 2's and my former room was 14x18 with a ceiling vaulted to 10'. If you have placement flexablity and can use acoustic treatments as needed, bass traps being the most likely, you'll be fine. They sounded great in my room.