The Blender UI elements are incredibly small by default on high resolution screens on Windows (15" UHD screen). I found the Preferences -> System -> DPI setting which can be set up to 144. This makes Blender usable, but still uncomfortable and difficult on the eyes. Is there a way to make the UI elements even larger?
To make the UI elements even larger you can choose Double under the Virtual Pixel mode this option is in User_Preferences->system
Another thing that is very useful is to hold down Ctrl and the Middle Mouse Button to rescale various panels. This is the same for the 3D Viewport when zooming in or out to view a model. The Outliner Area is the only place I've found so far where this does not function yet.
By pressing the HOME key on your keyboard, you can reset the resized panels back to the original default size.
Hover the cursor over one of the panels and hit Numpad + or Numpad - keys on the keyboard to change the size of the font and UI elements.