/usr/src/linux-headers-4.15.0-20/ is in linux-headers-4.15.0-20 4.15.0-20.21~16.04.1.
This file is owned by root:root, with mode 0o755.
There are a lot of files here (18208 total).
We're only showing the immediate contents of /usr/src/linux-headers-4.15.0-20
.