There are a few things that can cause DW to slow down like that...
1. Code Errors, run the validator at http://validator.w3.org/nu to make sure you don't have any structural defects in your html. Little things like missing alt attributes or obsolete width attributes won't be an issue, but missing starting/ending tags can cause the newer version of DW to throw a fit
2. Protocol relative links (starting with // rather than http or https) to fonts or scripts in the head of a page can cause issues. Turn them into http and see if that changes anything.
3. Externally referenced scripts in general. Sometime, for reasons I've never been able to figure out, DW will just "not like" a script on a remote server. You can try commenting out all scripts with html comment tags and see if the pages open right. If they do, un-comment one at a time until you find the culprit. Make a copy of that file locally and link to it during development. Change the link to the remote file as a last step before uploading