We have 45,000 pages in our WP Admin. After around 20,000 we started noticing the time it takes to edit a page increased. What we’re seeing now is that it’s taking around 1 minute to fully open a page to edit it. Now all other areas of the site are running just fine. Editing posts are fast. It’s only when editing a page that it takes a long time to open that page to edit it. We noticed that the more pages we have the slower that open edit page takes.