Para SLE 15 SP2 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/devel:languages:python:backports/SLE_15_SP2/devel:languages:python:backports.repo
zypper refresh
zypper install python3-Pillow
Para SLE 15 SP1 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/devel:languages:python:backports/SLE_15_SP1/devel:languages:python:backports.repo
zypper refresh
zypper install python3-Pillow
Para SLE 15 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/devel:languages:python:backports/SLE_15/devel:languages:python:backports.repo
zypper refresh
zypper install python3-Pillow