Para 15.6 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:bs-team:openSUSE:open-build-service:PR-13492/15.6/home:bs-team:openSUSE:open-build-service:PR-13492.repo
zypper refresh
zypper install obs-server
Para 15.5 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:bs-team:openSUSE:open-build-service:PR-13492/15.5/home:bs-team:openSUSE:open-build-service:PR-13492.repo
zypper refresh
zypper install obs-server
Para 15.4 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:bs-team:openSUSE:open-build-service:PR-13492/15.4/home:bs-team:openSUSE:open-build-service:PR-13492.repo
zypper refresh
zypper install obs-server