I had this same problem. I reduced the file size somewhat by doing this: (1) In
storyboard view, select all, right click, video quality and set it to STANDARD.
(2) In edit view, click View Library and click the Select Unused Items icon
(next to the trash can) and delete those. It may also help to get rid of
duplicate files ("copy of. . .") but be careful with that one.

Good luck.