Jackson has never much minded the cold. In fact, he prefers it. However, it's never been -15 here, LOL. The coldest it generally gets is 20 degrees F, IME. Of course we've had colder but it's somewhat rare.
But this dog LIVES for snow... the only time I've seen him really cold is when the wind is blistering or there is a blizzard and he's been running through deep snow for long periods of time. Also, if he's sitting still in the cold, he will sometimes shiver (i.e. not being active). Otherwise, most of the time, I put a coat on him just to make myself feel better.
He hates the rain though!
Brit & Jackson
It's Beginning to Look A Lot Like Christmas