How to fix the 60 to 30 FPS jump in BioShock 4 underwater scenes?

It was unbearable; in such a beautiful underwater world, the VRAM bottleneck caused the frame rate to swing wildly between 60 and 30 FPS. I tried increasing virtual memory to 32GB, which stopped the crashes but didn't fix the stuttering, making the attempt feel like a superficial fix. I used the GamePP Resource Scheduler to set the game's VRAM priority to Highest and cleared 6GB of system cache. Now, frame times are stable at 14-20ms per RTSS, VRAM temps are 62-68℃ per HWiNFO, and usage is 7.6-7.9GB per GPU-Z.