It sometimes takes FIVE minutes for the Edit page to load. This is unacceptable.
We hope this is fixed soon. It is on the WP side, not the server side.
No, I'm sorry, but just, no.
No page can take five minutes to load and it not be a server issue. Period. Five minutes is ridiculous. So ridiculous, that your server is misconfigured in a way that causes something to block for ridiculous timeout periods. Heck, default PHP installations won't even RUN for that long, they cut out after 30-60 seconds.
In other words, the only way that you get a multi-minute page load is that something WordPress is trying to do (contact another site, do a DNS lookup, could be anything) is causing your broken server to sit there, waiting for an answer that will never come, over and over again.
"Slowness" is not a specific enough problem for us to solve. Nobody here can likely help you solve it either. And it's not a problem with WordPress.
You need to find a) somebody who knows servers, b) somebody with access to your specific server, and c) somebody who knows PHP and have them debug this for you. Because something on your server is badly broken, but it could be any damn thing so there's no way for us to narrow it down. You have to narrow it down. Once you know what the actual problem is, THEN we can judge whether or not we can do something about it. Even then, it would be, at best, a detection and workaround to servers with your specific problem, not a problem in WordPress itself. The problem still would need to be fixed on your server.
But until we know the problem, we can't even work around it. And if you can't tell us what the problem is, then we have no way to magically guess WTF is wrong with your box.
That's just how it is. Sorry.
If this is unacceptable to you, then I suggest that you switch off WordPress to something else. Not that it will help you any, really, but hey, worth a try.