For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Leen-Meyer:unverified/15.5/home:Leen-Meyer:unverified.repo
zypper refresh
zypper install libcap
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Leen-Meyer:unverified/15.4/home:Leen-Meyer:unverified.repo
zypper refresh
zypper install libcap
For 15.2 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Leen-Meyer:unverified/15.2/home:Leen-Meyer:unverified.repo
zypper refresh
zypper install libcap