Ya don't over think the 15w40 conventional. Many, many people use it year round up here with no ill effects. If it gets cold, plug the vehicle in.
2006 Trailblazer LT. Castrol Edge with Fram Ultra.
2017 Ram 3500 SLT Megacab. Duron SHP 10w30 with Hastings LF608.
1993 GMC 1500. It has oil and still runs