Watts = Amps * Volts.

15 watts per channel = 30 watts = X * 14 volts
30W/14V = 2.1 Amps.

So, I like to have a bit extra, so, I want at least a 3 amp 14 volt power supply. If you can find a wall wart which meets these requirements, go for it. I like the idea of a shielded (metal case) converter/power supply.

Enjoy the Music. Trust your ears. Laugh at Folks Who Claim to Know it All.