Tempratures in the UK don't translate to North America/Most of Scandanavia/Eastern Europe. -5c in the UK is generally really really fucking cold, because its so wet. -5 somewhere dry and inland can feel warm. In Ukraine earlier this year I was walking around in just a long sleeve shirt despite it being -7/-10c out. It was genuinely too warm to have more on if I was moving, though on other days it'd be -1/-2c and it was genuinely fucking freezing.

Though when its really cold, its really fucking cold no matter what. But -15c on the coast with wind blowing from the sea is 100 time colder than -15c with still air 300miles from the nearest body of water. I haven't experience below -15c outside of commercial freezers which I never found cold as I was never in them long enough, and usually they were a refuge from a hot kitchen so the -20c was welcome.

Another thing, you can get used to the cold really easily too. Which is something thats bizarre. But having shit like cold showers and only wearing more than a t-shirt if its likely there may be some amount of danger from being in the cold while get you silly comfortable with the cold.