Excruciatingly slow website performance

Hi this is a strange on. I have 6 identical sites with the same plugins, themes and pages (just with a little different page text/logos) all running WordPress 4.6 with Wordfence.

The sites all load up really quickly and run off the same dedicated server etc. But 1 of the sites loads up extremely slowly. Where all the other sites load within a second or two, this site takes 20-30 seconds to load and similar from page to page. It is also just as slow in the backend too!

It has exactly the same options and features enabled as the fast sites so I can’t understand why Wordfence is killing this one… If I disable Wordfence it loads up no problem, nice and quick again.

The only difference I can see when clicking through all the dashboard option pages is that there are more firewall rules on this site than the others. A lot more, for no obvious reason. There seems to be no way to remove them or change the rule set, and if I put the firewall into learning mode again the sites still doesn’t load any quicker.

Any help really appreciated to fix this. I don’t really want to turn off live scanning or change other options as I know the other sites load really quick with all this enabled. So I believe there is a problem with Wordfence on this site, not the server/site itself.

Thanks again.