1500w if on 110v --> asking for trouble, just to be safe, on 220v, any 16amp socket should run only 8amp x 220 = 1500w maximum 24/7. Cables should be always 50% more room, if a cable is 20amp then always use maximum 10amp, to have the right and safe procedure is very expensive but you will not burn your house if something happens.
to sum this up, breakers are meant to protect the wires. 50% is the safe zone because at 60-70% even if the breakers does not trip from time to time, breakers tend to be warm and get cooked/burned in long 24/7 usage
for me i pushed the wire to ~65% and increased Amp rating of my breaker (push limits only if you know what you are doing)
- not part of the building wiring (mining dedicated wiring)
- i know my wires, the breakers, the load
so far so good.