linux-source-4.15.0 4.15.0-20.21 (amd64 binary) in ubuntu bionic

 This package provides the source code for the Linux kernel version
 4.15.0.
 .
 This package is mainly meant for other packages to use, in order to build
 custom flavours.
 .
 If you wish to use this package to create a custom Linux kernel, then it
 is suggested that you investigate the package kernel-package, which has
 been designed to ease the task of creating kernel image packages.
 .
 If you are simply trying to build third-party modules for your kernel,
 you do not want this package. Install the appropriate linux-headers
 package instead.