RE: 15 yards, broadside, no obstruction--no shot!
Dave,
You could've drawn, or at least gotten ready, at 100 yards when you noticed he was on a rope.
As you know, deer do not have good vision. At 100 yards, he would not have spooked (IMO) with slight movement 20 feet off the ground.
I'm just curious...from this tree, how do you normally draw and release if your so skylined?
Perhaps you had the "monster fever"...[8D]