For a 15A breaker, you can use about 12.5A
Or about 1500W
Use more 15A circuits to the breaker box rather than less 20A circuits
This will let you somewhat isolate things better.
Don't go by Rated output watts, go by power draw watts. A sticker on the back of the amp should say the power draw.
Given 1500W - look at 50% efficiency for older amps, 90% and higher for class-d.
Account for cooling - you're going to need it. That other 50% is pure heat from the amp.
Use LED lighting and everything as efficient as possible to keep the BTU's down.
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