The page in question takes a full minute to load. But only for one client, and I only have access to that clients sandbox.
If I was developing normally, I would use the Developer's Console and logs to determine why a Visualforce page loads very slowly. However the slowness only occurs for one client. They are a very large company and have thousands of users and fields and objects etc on Salesforce. I tested a few suspicious SOQL queries on the page, but found they all completed within .5 seconds.
I am at a loss as to how I can find the cause of the problem. I tried to get my developer account 'big' enough to recreate the issue but I could only create a max of 200 users and only 5,000 roles which was not enough to cause the slowness.
My current plan of action would be to make a few educated guesses about what the problem could be, make those changes, then get the client to install that new package in their sandbox. However, since they are large, they are slow :) and it could take weeks to install each package. I would like to be relatively certain I have a good idea what the problem is before I try random fixes that will take a long time to test.