Comment 6 for bug 1456730

It actually hangs for me on a fresh install of 15.04 along with 15.10
Attached journal log from 15.10.

The issue seems to be the inability to terminate the serviio.sh java process (PID1848)
Line 24190 is where the hang ends after the job to stop session-c1.scope times out:

Jun 04 17:35:32 m51ac-x systemd[1]: session-c1.scope stopping timed out. Killing.
Jun 04 17:35:32 m51ac-x systemd[1]: session-c1.scope changed stop-sigterm -> stop-sigkill

sigkill takes care of the process and shutdown can continue.
Note: serviio-console.sh is PID1918 and gets terminated much earlier on line 23124

It might be a bug with serviio but as you mentioned, the processes can be killed before shutdown,
no problem handling sigterm sent from terminal.