How to change timeout in systemctl

When I boot on my debian, startup hangs for approx 2 minutes on the line:

Loading, please wait...
[    5.191043] systemd-fsck[129]: /dev/mmcblk0p2: clean, 234192/873120 files, 2335263/3491328 blocks
[    6.645242] intel_rapl: no valid rapl domains found in package 0
[    6.643682] systemd-fsck[222]: fsck.fat 3.0.27 (2014-11-12)
[    6.664844] intel_rapl: no valid rapl domains found in package 0
[    6.660702] systemd-fsck[222]: /dev/mmcblk0p1: 3 files, 33/130812 clusters
[    **] A start job is running for LSB: Raise network interf...38s / no limit)

Eventually, it gives up on raising the network interface and continues booting.

Question: How can I change the timeout used in systemctl, so that after 15 seconds it stops trying to raise the network interface?

Additional info: the source of the problem is the use of a wifi USB dongle on this machine. Sometimes the dongle is there, sometimes it's not. When the dongle is not plugged, I expect the network interface to not being raised - and in this case I just don't want to wait for too long.