For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:urbic/openSUSE_Tumbleweed/home:urbic.repo
zypper refresh
zypper install sbcl
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:urbic/15.5/home:urbic.repo
zypper refresh
zypper install sbcl
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:urbic/15.4/home:urbic.repo
zypper refresh
zypper install sbcl