Not necessarily true though. 0w40 would be recommended if that was the case. There is a difference between 15w40 and 0w40. Never had a problem with fuel gelling down to 30 below (parked outside).40 is 40. Your engine doesn't get more protection from 15W vice 0/5W in the Summer.
Pick the 0/5W that is most convenient or gives you the warm fuzzies and worry about fuel gelling in the Winter instead.
Talked with Mobile 1 and they recommended the Delvac 1 over the Delvac Extreme. Something about 3x OCI of OEM vs 2x, sound like marketing BS, but I didn’t realize it was Delvac vs Delvac 1, but either way, got 3 gallons of ESP 5w40 for $30 after MIR. Paired with the AMS Oil filter. I should be able to get to April or May next year and I’ll be really tempted to stick with the same 5w40 ESP, it’s cheap enough and I’ve seen lots of folks running 5w40 in hotter environments, without issues.