Для 15.5 запустите от имени root:
zypper addrepo https://download.opensuse.org/repositories/server:Kolab:16.1/15.5/server:Kolab:16.1.repo
zypper refresh
zypper install roundcubemail
Для 15.4 запустите от имени root:
zypper addrepo https://download.opensuse.org/repositories/server:Kolab:16.1/15.4/server:Kolab:16.1.repo
zypper refresh
zypper install roundcubemail
Для 15.3 запустите от имени root:
zypper addrepo https://download.opensuse.org/repositories/server:Kolab:16.1/15.3/server:Kolab:16.1.repo
zypper refresh
zypper install roundcubemail