It would appear that the Ubuntu 15.10 (Wily Werewolf) operating system has been rebased on the latest stable Linux 4.1 kernel branch, which is an LTS (Long Term Support) release that will get security patches and bugfixes for a few more years. Although tracking of the Linux kernel 4.2 continues in the unstable repository, there are no news if the final version of the Ubuntu 15.10 distro will be rebased on Linux kernel 4.2 or not.