Why does BioShock 4 stutter when my CPU is too cold (15-20℃)?

While diving, I noticed my CPU temp dropped to 15-20℃, yet the frame rate began to fluctuate inexplicably. I tried locking the voltage in BIOS, but the extreme temperature difference caused micro-condensation on the base, which made me very uneasy. I used the GamePP Fan Curve Configuration to drop the TEC power from 100% to 65% and set a 30℃ minimum floor. RTSS showed frame times stabilized at 9-12ms, and AIDA64 confirmed a safe operating temperature of 35-42℃ with memory at 38-42℃.