Playback slows down on a project with many files

Hello. I have a constant problem on all versions of Premiere. When there are 100-1000 video files in a project, everything is fine. When there are 1000-5000 sources in a project, playback starts to slow down wildly even when just viewing files. The timeline is clean, no effects, but it slows down viewing files very much. A solid slideshow even when viewing proxies. It is simply impossible to work.

I checked the problem on a new project. To do this, I added 100 files from a large project to a small project. Both projects are open at the same time. In the large project, everything slows down terribly in the source monitor window. At the same time, I view the same files in an open small project - everything is fine.

Of course, I cleared the cache. On huge projects, the problem occurs after a few hours of work. On large projects, after a couple of days. When a lot of subclips appear in the project and the timeline is filled, then playback starts to slow down wildly and nothing helps. Tell me how to solve this problem?