Last winter at -30C I never plugged it in at work and had no problem starting my 2014. So far this winter at -23C no problems either. Mine is parked in an unheated garage over night.
My manual indicates plugging in at -10C and lower, so as a new owner of a 2015 I have been putting it on a timer from 5am - 10am , as I don't need to have it sucking hydro all night..