Most of our stands are 18'-22' off of the ground, with one that is about 5' higher which is primarily due to the tree itself having an irregular trunk in the height range we would normally use. I also try hard to select trees that have some sort of additional concealment due to the terrain and/or adjacent trees/foliage. We rarely get noticed at this height.
FWIW, I visited a prime southern Iowa farm this spring where a well known hunter spends his "tree time" every fall and I was very surprised to see how low many of his stands were. Several were no more than 8'-10' up and at least one was low enough that I could stand on the ground beneath the stand and stretch and touch the bottom of the platform. Now that's low!
All of these "low boys" though had excellent cover and/or additional concealment. Several were cut into cedars, which provided for very effective adjacent cover.