/usr/src/linux-headers-4.15.0-46-lowlatency/.12303.d is in linux-headers-4.15.0-46-lowlatency 4.15.0-46.49~16.04.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1
.12303.tmp: /dev/null