Emulated game starts lagging as game progresses

Can someone help me fix the lag. I'm emulating zelda twilight princess and it was running completely fine until I got about about 8 hours in, where it started lagging and stuttering, and it has gotten progressively worse. When I start a new game, it is completely fine again though. I can't seem to fix it, and lowering the graphical enhancements isn't working anymore. Please help.

CPU: Intel Core i7-7700 3.6GHz

GPU: Radeon RX 580 Series

RAM: 8 GB