Treestand hunting elk is a VERY good idea. I just shot my cow elk this year on opening day out of a tree stand. My buddy shot his out of a different treestand on the 8th of Sept. He had opportunities each day and finally connected. he also had a couple big bulls beneath him (but, no bull tag).
If wind is a problem, get up as high in the tree as you can go. Even with good wind, 15 feet is not enough! Elk do look up, unlike most deer. At a minimum, you should be 20 to 30 feet above the base of the tree. Also, if possible, make sure your tree is on the uphill side of the trail or area you are anticipating the bull to come from. This will also help keep your scent up higher in the trees.
Just remember, you will be shooting downhill and your arrow will not drop as much. My buddy actually missed his first shot and the elk came right back. He still shot high on the second shot and "spined the elk. Dropped her like a stone but he had to hurry up and climb outta the stand to finish her off thru the vitals.
Also, if you go to "ElkNuts" web site, he has a book about treestand hunting RM Elk. The guy that wrote it is 95% successful taking elk every year from his tree stands!