A sidestep from the original post but can anyone confirm if the current downloadable
SLE-15-SP1-Installer-DVD-x86_64-GM-DVD2.iso
from SUSE is
a: bootable
b: valid for upgrading offline a minimal SLES15 on its own.

I have downloaded several times and verified the checksum.
System does not want to boot from it but can boot from
SLE-15-SP1-Installer-DVD-x86_64-GM-DVD1.iso