No, drafts, by definition are cold breezes that hit directly upon the hens, particularly while on the roost.
Ventilation is provided at the top of the coop, air escapes, taking humidity with it. I serves the same purpose that you have vents on top of your home. This lets humidity escape...
My chicks do fine at much, much lower temps than 15. First, I only keep hardy breeds. That's number one. The list for cold hardy birds is quite long and most hatcheries and other breed information sites do a good job of giving you that information.
Barred Rocks are pretty darn hardy birds...