Bronko is right in what he's saying. From 15' up and shooting at a target 30 yards out your range finder will read just about 1 yard farther (actually it's 1.8'), so even if you'd set your sight for 31 yards you shouldn't be more than maybe 1 1/2" high. Anything closer would have less variance and the farther out you shoot the downward angle becomes more horizontal.
Let's use 20 yards (60') as a more normal figure and about 18' up as this is about where the bow will actually be from a 15' treestand. The visual distance (hypotenuse of the triangle) will be 20.88 yards. Either way, not enough to make but the very slightest difference in point of impact.
There are two things that will make a person shoot high from a treestand. One is by lowering the bow arm instead of bending at the waist. Doing so misaligns the "T" shape of the upper body, shortens the draw length and changes how you see through your peep. The second is the angle at which you are observing the animal. The closer it is the steeper the angle and the narrower the vital area becomes.
There is a third reason many shoot high on an animal or even miss. That is due to noise made by the bow and/or accessories. The deer hears whatever noise is made, crouches, loading it's muscles to flee. No bow is fast enough to compensate for this so the best thing is to have a bow that is absolutely quiet so as not to alarm the animal.