Slow Backups [of Outlook .pst file using Synchback]

I use Syncback for my backups from one computer to another. All of my backups work very smoothly and fast except for my Outlook folder (pst, etc.). It takes about 30 minutes!! Synback is unable to find an issue and in fact when I've checked with them from time to time to see if anything new may have come up, they're downright rude to me. Does anyone have any ideas why only the psf folder would be so **** slow? Most of my backups are from my master computer to other computers and equipment. The pst is from my slave to my master. the slave is attached via a hard wire to the router.

 

The actual pst is 517,841kb. then there is the backup of similar size if I didn't remove it in the filter and a couple of small files.