It runs slow.

From the time I started using program until my last project (a week ago), it has never been this slow. There's now a red line above my timeline, and I have to render every clip for it to play with any level of smoothness. No one asked for these changes. My computer isn't very powerful, but at least I could edit without issue before now. I only had slowdowns when there was a lot going on in my timeline. Other than that, it was fine. Now, it has become unnecessarily onerous and annoying to use this program. Please fix and revert it back.