saby:

Peter, the path you give for "hidden" render folder is the default path of PS15's (and prior) auxiliary files.

Why do you call it "hidden" render folder ? 

 

Program Data is a hidden  W7 OS Folder, here. Therefore the Render Folder is hidden, Saby

I have my Program Data Folder Unhidden in Screenshot, that shows as  a feint Yellow Folder. If I were to Hide it again, Folder would disappear..

Studio has 2 Render Folders. 1 Unhidden & 1 Hidden. IMO, you can select the Directory where the you want the Unhidden Folder to go, but not the Hidden

Studio File / Delete Aux Files only Deletes those Aux Files in the Unhidden Render Folder. Not the Hidden.

Screenshot: