One more thing (I don't know if anyone said this or not):
Your max load on a 15A circuit is 80% or 12A. If you exceed that, the breaker will likely trip (or even if you get close to 12A).
Your max load on a 20A crkt is 16Amps.
This is a general rule and some exceptions can apply.
What you are doing is providing 125% for continuos duty (longer than 3 hours) and also you are building in a safety precaution by only going 80% as required in art. 220.
Anything at or near 12A requires a 20A circuit.
