Why does The Sims 5 stutter when loading new communities?

I was frustrated by visible lag in The Sims 5. I tried clearing temp files, but background processes still used 12.5-15.2GB RAM (Task Manager). I used GamePP Resource Scheduler to set priority to Real-time. RTSS showed frame time dropped from 9.1-13.5ms to 5.8-7.2ms. AIDA64 confirmed stable 55-60℃ memory temperature.