After upgrading to TPAM 2.4 or 2.5 from previous version, peformance is noticeably slower when Listing or Filtering objects.
One major cause of this slowness could be the continued use of Global Groups for assigning permissions. They have remained in newer versions for backwards compatibility, but should be disabled if not required.
The impact that the Global Groups have on performance is not dependent on the number of users that are contained in the group. They can be large or small. It is simply the addtional burden that that is put on the filtering process by having to include these types of groups at all. It's mostly due to the redesign of the permissioning system that was introduced in version 2.4.
Creating a Group of all your users and a Collection of all your Systems and assigning an Access Policy of one to the other will accomplish the same thing as a Global Group and should have less of an impact on your performance.
Further information can be found in the Adminstrator manual, in the sections that discuss Access Policies and permission related topics. There are instructions for how to set these things up.