Are you still able to reproduce after upgrading to latest stable version 2.25.7?
There are some improvements in it when having many projects, see 0032131

Test 2.25.7 and it does not help.

I know where the problem, it builds of the project tree. It builds every time for calling function, so I have many times while the server builds the project tree for one request of page.
The subfunction cache data from the database but the main for building the project tree does not do.

I create a pull request later.

PR https://github.com/mantisbt/mantisbt/pull/1900

@nhchoudhary please have a look a the discussion in https://github.com/mantisbt/mantisbt/pull/1900.

I'm reluctant to merge it as-is, because I am not able to reproduce the original performance issue and therefore can't properly review and test the updated code.

Since you mentioned in 0032790 that you faced the same issue and the proposed fix did improve things for you, maybe you would be able to provide a reproducible test case that I could look at and use for tests.

Your feedback, here or directly in the pull request, would be appreciated.