I'm having the same issues on the XPS 15 9550.
I've no idea what to set the resolution or scaling to. Some applications look ok and then I install some of my required software and it looks terrible, really small text and buttons..
Did you ever come up with a solution?
My Dell XPS 15 9550 has exact the same problems as macartanmcquaid and others described. What is the point of having this awesome screen if you cant use it.
Did Dell ever came up with a solution?