You need to do some research on circuit breakers, what you said is incorrect. A 15 amp breaker will trip at 80% of it’s 15 amp rating which is 12 amps, but that’s continuous, breakers are time sensitive. A lot more than 15 amps for short durations can and does happen without the breaker tripping.
Actually a 15 amp breaker will pass 15 amps continuous load all day long without tripping. Some breakers more than that.
NEMA Standard:
Breaker rating 0-30A. Allowable Trip Time.
A 15 amp breaker must, supposed to, trip at a continuous 20.25A , (135%), in 1 hour.
30 amps continuous, (200%), in 2 minutes.
Must... Hopefully will...
A loose wire to breaker terminal connection, will cause heat to be generated in the loose connection and will transfer to the thermal unit in the breaker, causing the breaker to trip at current lower than 15 amps.
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The breaker doesn’t see VD, (Voltage Drop), that may be created on the branch circuit wiring because of the connected load. Or the power supply of an amplifier being pushed hard, playing a high dynamic music as it pulls short bursts, (gulps), of current to resupply current, (actually I believe it's electrical energy), to the electrolytic caps. Power amplifier’s power supplies like a steady state line voltage.
