/usr/src/linux-source-4.15.0.tar.bz2 is in linux-source-4.15.0 4.15.0-45.48~16.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-source-4.15.0/linux-source-4.15.0.tar.bz2
/usr/src/linux-source-4.15.0/linux-source-4.15.0.tar.bz2