How to stop thrax lagging like crazy?

I'm on pc and for some reason the thrax fight lags like crazy. My pc can run games like fortnite perfectly well at high fps but thrax just destroys it. Even on lower resolution and minimum graphics settings it still knocks my fps down from like 100 to 15. Does this happen to anyone else? This is for the entire area the thrax is in btw, even before he spawns.