Having serious playback and exporting issues with LOTR 2 Towers (Patreon)

First time using the Brio 4k. I chose the 1080p30fps setting and the mic settings at 48000Hz .wav file... which is normally fine. But for some reason editing this video is taking REALLY long because of playback lag....and I exported a 5 second blooper from the full-length video, and that took around 5 mins to export... That is extremely worrying for me because something like that should literally only take 1 second ... :/ Cannot imagine what exporting a 4hour long video is gonna be like, but I have a feeling it won't be done by today >.<

If anyone has a workaround or knows anything (more than I know) about video editing then please let me know. I have done all the obvious things and have no clue what's wrong :/