Hello @disuye,
I tried your code and it is stable for 151 fonts with Processing 4.0b8 and W10 Pro.
Software used:
https://visualvm.github.io/index.html
My experience with System.gc():
https://discourse.processing.org/t/pimage-garbage-not-being-properly-collected/12252/4
https://discourse.processing.org/t/insufficient-memory-for-java-sketch-on-raspberrypi/12331/2
:)