For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/spins:invis:15:unstable:samba/15.6/spins:invis:15:unstable:samba.repo
zypper refresh
zypper install samba
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/spins:invis:15:unstable:samba/15.5/spins:invis:15:unstable:samba.repo
zypper refresh
zypper install samba
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/spins:invis:15:unstable:samba/15.4/spins:invis:15:unstable:samba.repo
zypper refresh
zypper install samba