Starting the game activates steam vr and makes it run slow, is there a UE setting that got checked saying it's a VR game?
No. Unreal Engine games always trigger SteamVR. SteamVR thinks that Unreal Engine games are always VR games. If you want to get better performance, close SteamVR after the game boots up. That should fix your problem. If the game quits after you close SteamVR, then minimize SteamVR and try playing the game. Hope that helps! :)