I'm sorry but, I can only confirm that, with the December update, the cache is no longer intentionally recreated at each start, but only if anything in the Scenery Library changes.
It's possible the problem is caused by your antivirus, which has blocked the last update to be fully installed. This would explain the 5 minutes cache regeneration, which is unheard of ( takes no more than 5-6 seconds here ), which is caused by the antivirus scanning each and every .BGL in your system, just because GSX is accessing the files.
Configure the antivirus to add the following folders to the antivirus Exclusions:
- The main Addon Manager folder ( where you installed GSX, by default C:\Program Files (x86)\Addon manager
- The FSX own folder. I personally exclude the entire Steam Library, all your games will load faster and better this way.
- Every other folder that is not inside FSX that contains 3rd party sceneries.
After you do that, run the FSDT Live Update again, to be sure you get the latest update in full. The cache WILL be regenerated after the update ( this is normal, after an updated ), but shouldn't after subsequent startups, unless something in the Scenery Library REALLY changed.