I plan on hunting from a treestand about 12-15 ft. high. How much of a difference with my arrow flight/path be than opposed to shooting on flat ground?

It all depends on the technique. Bend at the waist and most of all, practice from an elevated stand!!!!!

Usually a couple inches. Some people say theres doesn't change at all but probably 2-3inches.

Good advice. Don't cheat by lowering your bow arm. As far as accuracy, you should plan on practicing from elevated stands to make sure everything is working properly before you hunt. The difference is not much up to 30 yards or so.

as above if you are going to hunt from a treestand then you should practice from a tree stand or elevated position. I was watching a show about a guy giving tips about hunting tree stands which he always hunts from so during the off season he practices off his garage and shoots at his 3d target in his backyard. it was kind of funny because here is this guy in full camo shooting from his garage while his neighbours are bbqing next door think oh my god what kind off neighborhood did we move into(sorry a little off topic)

I've never noticed a difference. I aim just as I would if on the ground.

BUT, I also sight my bows in low, compensating for the tendency to shoot high at extreme angles.

The no-peep also helps with up and down hill shooting.

i wouldn't worry about it at 12-15'.

uphunter15 is right on the money. Draw your bow straight out in front until your at full draw and into your anchor. Bend at the waist and your arrow will impact on your aiming point. Another thing to remember from a treestand is the closer the target is to your stand the smaller the target. You have about 18" on a broad side shot. Less than 12" on a steep shot close to your stand. Try to wait for the animal to be at less of an angle if possible. You stand a much better chance of executing a precise, vitals shot.

There are a lot of good suggestions on here.

Just bend at the waist and practice.