I've watched a few youtube vids on it and it sounds pretty awesome for a 15w. You can really hear the tubes working in the lil mamba. Anyone own it or played it before? I'm really thinking of getting it. I wanted a Super sonic 22w but its too loud for my room and I dont have a band. The 15w seems the more logical choice, plus its tube which is perfect.
Don't judge an amp by its power. Smaller (less power) tube amps are likely to sound better than bigger ones, because you can work the valves harder.
Also, a 22 watt amp is not going to be any louder than a 15 watt amp, remember, you need 10 times the power to double the volume, i.e. through the same speaker, a 150 Watt amp is twice as loud as a 15 Watt and a 30 Watt amp is only noticeably louder than a 15watt.
I have an 18 watt amp that has adjustable power, and I almost never gig it set to more than 5 or 6 watt. I have also gigged with my Blackstar HT5 which is a little 5 watt 'practice' amp.
So if you like the Supersonic better, get that one instead.