It looks the file gets corrupted when it copies. I made a Linux Mint Virtual Box machine so I could access it via NFS, and I verified from SSHing into the server, that both show the 15 GB file as only 4.3.
So at this point, I am going to copy the file using the VM with NFS to see if it copies and the Windows PCs can see it.
If this does work, are there any ideas why copying these large files with Windows corrupt the files?
I think I found the problem:
I had this in the config which I think was causing problems: