Moodle expert needed

I need a Moodle expert to sort out the folowing problem on my Moodle site: My primary admin login is VERY slow, sometimes takes more than a minute to log in. If I create another admin user, that user is not so slow. If I then change that new admin user to be the primary admin, that user becomes slow, and the original admin user (then no longer the primary admin user) login becomes normal. I therefore conclude that the problem is with the primary admin. Please only bid if you have experience in troubleshooting Moodle for this kind of problem. Please put relevant experience in a PM.