15A vs 20A is a factor of the gauge of the wires as well. You can’t just swap the breaker for a bigger one. You’ll get heat and depending where that could burn the house down.

I have a relative whose house burnt down due to stapled wiring in the attic. Thermal cycling eventually created a short. When your attic catches on fire the smoke alarms go off in time to save the people, but the moment the ceiling starts to cave in the entire house is involved and you’re mostly trying to keep the neighboring houses from burning.