I found when page included a lot of attachments, such as more than 400, the page content will load slowly or open attachment slow. Is there limit for attachment number in one page? Or how can I adjust it? Thanks a lot.
Technically, there's no hard limit low enough for users to run into, you can add millions of files if you want.
But when you load a page, Confluence has to read everything on it in order to give it to a browser, and your browser has to render it all. If you've overstuffed a page, then of course it's going to be slow, especially if your page is displaying the content of the attachments.
There is no limit to adjust, you just have to educate people not to write vast pages that will be slow to render.