The Preview button can not be used for biggers projects, because there is just too much media in it. What is needed is a preview on the folder you selected.
It should work a little like in Windows, if you change the view of a folder - to "small thumbnails". You do not get all images from your computer, just the ones from the folder. Otherwise editors will never use it.

The current folder is even shown beneath the content. The preview work in the context of the current folder.

This is essential for the Airbus Group relaunch project.