The ping on your IMAP server is fine so I suspect the problem is at your end.
Hiding messages marked for deletion will provide a temporary fix but isn't curing the problem - your inbox will still gradually fill up with messages, even though you can't see them, slowing matters down even further.
To sort this out further would require some hands-on with your PC. If you want me to try that, and of course I realise you may not want to take that risk, you can install an excellent piece of free software called TeamViewer (
www.teamviewer.com). That would allow me to control your PC remotely while you watch. We could then set up a convenient time to have a go at finding a proper fix. Let me know if you want to try that.