PIE will not duplicate already loaded actors in the editor, they are always streamed from disk, unless they have unsaved modifications. So it’s normal that it has no impact,
Make sure that the size of your cells and the loading radius, otherwise you can be loading the whole world when entering PIE. You can use the console-command wp.runtime.toggledebugdraw2d to display the loaded cells. Once that’s properly set, it should be quite faster en enter PIE.