I play an 85 Watt Boogie Mk IV in my living room, and it sounds fantastic at any volume. It's also got 2 12" EVMs
So, 'is 15w too much' has a couple of answers depending on a couple of important other points.
If you've got a master volume and a channel volume, you can use them to get the desired breakup you want at a volume you can stand. This is of course dependent on the quality of the amp
If you are running your 15Watter into a 1x8 cabinet it will also obviously be lower in volume at the same settings than if you are running it into a rectifier 4x12. For the biogger cab, you may need to go a little louder because it simply may not respond on "1" if the amp is 100Watts, but if it's less than 20 it shouldn't be an issue.
For whatever reason, tube watts always seem considerably louder than solid state watts. I don't actually care about the reason, just pointing that out. lol
So, Yamaha makes the THR5, which is 5 watts and has some cool stuff built in. Almost all the big tube amp companies make low wattage amps now too, like Mesa (has a few, actually, like the AMAZING Mark V:25), Peavey, and Marshall (the Jubilee 20W is particularly nice). There is the Blackstar HT5, Bugera G5, Victory Kraken, and I have recently heard very good reviews of the 20w Friedman Runt. But seriously, unless you are looking at an old 60's or 70's era amp with only a channel volume, you should be able to make ****ed near anything sound good at bedroom levels without too much hassle. A decent OD pedal and a chorus (or a cheap multi effects) and you are good to go.
Get the amp you like would be my suggestion, and make it work. It won't be difficult with a 1x12 or 2x12 setup.