5-7 seconds it's quite good and entirely normal if you don't have an ungodly large amount of scenery installed.
The cache regeneration, however, is not something you are supposed to start manually, because normally GSX will automatically detect a change in the Scenery Library. The only time you will probably need it, it's if you removed/renamed an AFCAD file in an existing scenery, rather than installing/removing a whole scenery, because in order to speed up the cache regeneration, GSX will not check each file one by one, but it's only checking the folder last modification date, and this doesn't change if you only remove/rename a file.
That's what the manual cache regeneration option does. It won't automatically let GSX magically find the AFCAD you would like to use, because the choice of the AFCAD file it's driven by the same logic of the sim itself: the one with the highest priority for any given airport will be used so, be sure you scenery has an higher priority than anything else that might conflict with it.
By checking the GSX parking customization page, you will see the name of the AFCAD in use by GSX, which might give you an idea why the correct one hasn't been selected.
