For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ojkastl_buildservice:lego_acme/15.6/home:ojkastl_buildservice:lego_acme.repo
zypper refresh
zypper install lego
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ojkastl_buildservice:lego_acme/15.5/home:ojkastl_buildservice:lego_acme.repo
zypper refresh
zypper install lego
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ojkastl_buildservice:lego_acme/15.4/home:ojkastl_buildservice:lego_acme.repo
zypper refresh
zypper install lego