We haven't had -15° and I hope we never do. I think -4° has been our lowest actual temp. Have had several -15° -20° wind chills and those suck. None of my cloths combat those temps well.
I'd take the 115°, maybe. Depends on the real feel. Once we're over 100° here our humidity adds another 10° to 15° for the real feel.
I found it so odd when another member from Arizona would say their 110° real feel was like 100° because of lack of humidity.
I looked into once and it said our humidity made hot feel hotter and cold feel colder. That ain't cool at all.