Welcome to the Community,
VMware supports virtual disks with up to 62TB, so you should basically not have any issues with doing a snapshot based backup.
There's unfortunately no way to calculate the snapshot size. The required (temporary) disk space for the snapshot, depends on the guest OS changes. A snapshot/delta .vmdk file starts with a small size (a few MB), and stores data blocks which are written while the snapshot exists.
With the 2TB (20%) free disk space, you should be on the safe side unless the data change rate is extremely high on this server.
André