Recently upgraded from 14.04 to 15.04 and immediately noticed my boot times went from 10-20 seconds all the way up to 120 seconds.
Can confirm that systemd is at least part of the problem, because if I manually select to boot using upstart (from the GRUB menu), the machine boots in 10-20 seconds.
Here is my systemd-analyze blame output: http://pastebin.com/iE3nrwRS
Here is my systemd-analyze critical-chain output: http://snag.gy/dX9q3.jpg
I will be happy to provide more information as requested.
Edit 1
I know this doesn't answer the question, but I think I am just going to permanently move back to upstart (something that works): https://wiki.ubuntu.com/SystemdForUpstartUsers#Permanent_switch_back_to_upstart
systemd-analyze plot > test.svg
on a pastebin – solsTiCe Jul 11 '15 at 16:55