How long do you think it takes to rebuild a corrupt 'calibre metadata' file on a kindle oasis 32gb, so at the moment there are over 3000 books on there.
Nearly 15 minutes is a bit excessive. How does the file become corrupted - I do not know, it happens quite often and I am extremely careful when it comes to plugging and un-plugging the kindle, I make sure all jobs are finished but still it corrupts for no reason at all, not often and not repeatable.
Maybe there is another method or some additional steps that can be taken to reduce this time. Backups come to mind, either on device or on the PC, or both and check which is newer.