Why does House Flipper drop to 15 FPS in crowded areas?

While idling in the main city, the normally stable 60 FPS would suddenly drop to 15 FPS with slight screen tearing, which was very annoying. I first tried lowering the memory frequency in the BIOS; while stability improved, the minimum FPS only rose from 15 to 20 per RTSS and overall performance dropped, which worried me. I entered the GamePP BIOS Load-line Voltage Adjustment Wizard and manually increased the memory voltage from 1.2V to 1.35V and loosened tRAS to 42. RTSS showed frame intervals converged to 10-16ms, and MemTest86 confirmed zero errors, with HWInfo showing temps at 42-48℃. Time to verify