15" wheels and tires would be quieter and more efficient if everything else was equal. But it is not! If you want a close match for the diameter, the same tire is seldom available (although you do want a different model for winter anyway).
But forgetting about efficiency, you want a narrower tire for winter use and I've confirmed that with personal use. I don't see any advantage in getting 15" tires for winter use, other than they tend to be cheaper than 16" tires. But huge advantage to going narrow, regardless of rim size.
2018 Kia LX HEV Metal Stream with Advanced Tech