For openSUSE Leap 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:so_it_team/openSUSE_Leap_15.5/home:so_it_team.repo
zypper refresh
zypper install R-base
For openSUSE Leap 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:so_it_team/openSUSE_Leap_15.4/home:so_it_team.repo
zypper refresh
zypper install R-base
For openSUSE Leap 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:so_it_team/openSUSE_Leap_15.3/home:so_it_team.repo
zypper refresh
zypper install R-base