Your images ran in 4.4 seconds/image on my 2020 Mac Mini M1 with only 8GB RAM.
For the Gap Fill do you have content aware fill check on when you run the batch? That will slow it down a lot…….
Also, try making new folders on the desktop for source and save and running a test there to make sure it isn’t a drive or folder issues. Based on your description, it sounds like there is a delay in opening the next file after it saves the last file.
Anyway, it is 10PM so way after hours now. We may need to do screen share tomorrow. Would 11 AM EST work? If so then please install the Remote Desktop app for google chrome. It is a free extension for Chrome. That will allow us to do a screen share. Then we can plan on doing it tomorrow if you are available.