For SLE 15 SP5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Kernel:tools/SLE_15_SP5/Kernel:tools.repo
zypper refresh
zypper install grub2
For SLE 15 SP4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Kernel:tools/SLE_15_SP4/Kernel:tools.repo
zypper refresh
zypper install grub2
For SLE 15 SP3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Kernel:tools/SLE_15_SP3/Kernel:tools.repo
zypper refresh
zypper install grub2