That only means it needs to check if there's a new version every 15 minutes though (e.g. by file hash or modification date), not that it has to download it agai

That only means it needs to check if there's a new version every 15 minutes though (e.g. by file hash or modification date), not that it has to download it again even if there's no changes every 15 minutes. I haven't looked into the cache settings though.