Admin pages take 30 minutes or more to load

I’ve tried installing Infinite SEO on one site with no problems at all. But on another site, the Infinite SEO admin pages take forever to load. Maybe 30 minutes or more (not sure — i literally fell asleep while it was loading… long day).

Both sites are multisite enabled, but the second site (the one with the problem) has roughly 68,000 more posts on it (the first has about 4,000).

Any ideas??