Albert Astals, okular's author, pointed me to
https://bugs.kde.org/show_bug.cgi?id=371887 . After the last ghostscript update
in openSUSE 13.2, okular can no longer open .ps files . I narrowed it down to
patch CVE-2013-5653.patch (
https://build.opensuse.org/package/view_file/openSUSE:13.2:Update/ghostscript.5742/CVE-2013-5653.patch?expand=1
) introduced in maintenance update ghostscript.5742 .

To narrow it even more, if I remove the lines that patch adds to gs_init.ps
from /usr/share/ghostscript/9.15/Resource/Init/gs_init.ps then okular works
again.
(that is, the two occurences of "systemdict /getenv {pop //false} put")

In any case, that goes beyond my knowledge of ghostscript, so I think it's
better someone else takes a look at this.