Ok, This might be helpful to someone.
In Ubuntu 15.10 guake has changed a little bit. To change your terminal to the right monitor you have to edit:
/usr/lib/python2.7/dist-packages/guake/guake_app.py
then change in line 831:
window_rect = screen.get_monitor_geometry(monitor)
by:
window_rect = screen.get_monitor_geometry(1)
kill and restart guake
Anyone knows a way to do this less hacky?