My save is 6,764 KBs. My character is level 16. The slow down only occurs when I load to exteriors from interiors, if I go back into the interior it is gone. No infinite loading screens, everything works fine. I thought I had solved it with uninstalling convenient horses but I just had it again. First time in a while. The lights were also flickering when I exited the cave this time, kinda like between vanilla and light mods I would assume but I don't know that.