If you are experiencing very slow opening of the test window, it's related to the number of tests that you have being recalled in the window.
This window can hang for a lot of time. If you reduce the number of tests which are being recalled it will open faster.
The way to reduce the number of tests is to complete schedules. What can happen is that after a while there are so many projects, with so many schedules and a lot of tests, which cause the system to slow down.