Ok, let's start off with some background. I'm starting to get into fulltime editing for youtube intros. At first, I made a few for a couple different games, in editing these I was able to use the preview at the full best 1080p 60fps quality and get no lag whatsoever. (Current time) I'm editing an intro for an unreleased game and I got some footage from him to use. Now suddenly my pc can't handle the footage in the same quality even with the preview window set to the lowest quality.
EDIT: It lags even worse between splits and effects
DISCLAMER: I know my writing flow is bad, so if you need more info let me know.