Fast bootup on fresh install 18.04.2 with kernel 4.18

[lotuspsychje]

Ubuntu 18.04.2 LTS up to date @ 17/5/2019 with kernel: 4.18.0-20-generic

I had ubuntu 18.04.2 installed with kernel 4.15(from the start 18.04.0) and experienced a very slow systemd bootup
and compared it with exact the same system on a fresh install 18.04.2 with kernel 4.18
wich was extremely faster.

Installing the HWE kernel 4.18 over the 4.15 system did not fix the slow boot, i had to fresh install
18.04.2 with kernel 4.18 and now it boots fast again:

lotuspsychje@RootBoX:~$ systemd-analyze
Startup finished in 2.948s (kernel) + 22.106s (userspace) = 25.055s
graphical.target reached after 22.098s in userspace

what could be the bottleneck for the 4.15 users?

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.18.0-20-generic 4.18.0-20.21~18.04.1
ProcVersionSignature: Ubuntu 4.18.0-20.21~18.04.1-generic 4.18.20
Uname: Linux 4.18.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.6
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri May 17 01:51:02 2019
InstallationDate: Installed on 2019-05-16 (0 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
SourcePackage: linux-signed-hwe
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.