Still on previous 4.15 kernel after apt upgrade to 18.04.2

You can upgrade kernel and keep it getting upgraded to future point Ubuntu releases by running

sudo apt install linux-generic-hwe-18.04

As for now it will install the 4.18 kernel.

I think you should be happy to stay with the 4.15 kernel series

From a conversation in an Ubuntu mail forum, an answer by Adam Conrad,

On Tue, Feb 05, 2019 at 11:53:22AM +0100, Nio Wiklund wrote: >

Will installed systems stay with this kernel series (like with the previous LTS releases) or will there be an automatic upgrade to the Cosmic kernel series and further until the next LTS kernel series:

If you install with 18.04 or 18.04.1 media and then upgrade, you will stay on the GA kernel and Xorg series. If you install with 18.04.2 or later media, you'll be on the rolling HWE kernel and X series.

... Adam

If you really want to upgrade to the new kernel series, you have to upgrade the hardware enablement stack, and it is risky. You should definitely not do it without a complete backup, so that you can easily(?) restore the system if the upgrade went wrong.

See this link: wiki.ubuntu.com/Kernel/LTSEnablementStack