Dell may well be working on a fix for S3 sleep with the XPS 15 9570, but the device still has numerous outstanding issues too. One such problem is high battery drain and overheating when asleep, and Dell now has a rather counter-intuitive workaround.
https://www.notebookcheck.net/Does-your-XPS-15-9570-get-hot-and-drain-its-battery-while-asleep-Dell-has-a-workaround-but-you-may-not-like-it.420400.0.html