Glad you found a workable solution.
However, all of the various video programs have their performance issues at times. Programs can react differently on different computers. See this link:
Perforance issues with Adobe Premiere Elements ... | Adobe Community
When you experience performance issues sometimes it's better to try to solve them rather than buying another bag of problems with some other video program. In your case I would have at least tried to re-download iMovie, or open in a new library, or open in a new user account, or boot up in Safe Mode and then re-boot in normal mode, do a disk repair with the utilities app, and so on. If nothing solves it, then that would be the time to consider another program.