Section Editors Slow TTFB

Hi, i recently upgraded a customer site to 3.14. Automatic upgrade would not run as i was running an older version of MySQL. To get round this I backed the DB up and created a new one in MySQL 5.7 and restored the data to it. After replacing the CMSB files and updated the settings file the site seems to have updated.

All my old sections appear to work fine but when i open the Sections Editor page in CMSB it's very slow to load (23 Seconds). I've tried re-uploading all the files in case something was missed but it had no effect. DevTools is pointing to a slow TTFB when the page is loading, any ideas on what i can do to fix this?