There are several reasons the system could be temporarily slow, but I don't have enough information from you to answer in detail. For example, is this a self-hosted solution where the server is the same as the viewing client? Also, when you mention "clips", do you mean videos? Is Files creating thumbnails for your video clips?
The server (which in your case may be the same as the client), could be slow when:
- Creating thumbnails for folders first time they are viewed. Imagine you have a folder with 100 images, and client scrolls fast, it would request up to image resize requests on the server, which will obviously require a lot of processing until cached.
- How large are your images? If your images are original 4000 px + images, each image will require much more processing, and will amplify the above exponentially.
- If you have video clips, Files uses FFmpeg on your server to create thumbnails. Another slowness factor.
- Folders need to get cached also, although that won't be as resource-hungry as the above.
All this is resolved with caching of course. Until then, the cache fragments need to get created, and there is no way to make that faster or less demanding. Normally, you won't notice much slowness, but it depends on your system and what else it is doing.