A couple of things that can cause lag problems in DW (while still being perfectly valid code)...
1. Protocol relative links in the <head> of the page. Check for links to scripts or fonts starting with // and change them to http versions, at least during development. If you don't have any https pages, you can leave them ad http: // versions permanently.
2. @import rules in your css. Rather than @import, use <link> tags to those css files in your <head> section.
3. Certain remotely hosted javasscripts can also cause problems. Try commenting out all scripts in your page with html comments...
<!-- <script> ... </script> -->
If the page opens without issue, un-comment the scripts one by one until you find the issue. Sometimes, just moving a problematic externally hosted script into the local site will stop loading problems.