/usr/lib/x86_64-linux-gnu/choreonoid-1.5/python/cnoid/Util.so is in choreonoid-plugins-base 1.5.0+dfsg-0.1build3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/choreonoid-1.5/python/cnoid/Util.so.1.5