I shot one last year about 9ft off the ground in a viper climber. What had happened, I borrowed a buddies summit(1st time) and when I got up about 15 ft, as I pulled bow up it came off pull rope.[:@] Time I climbed down and part way back up I was sweating real bad(over dressed). I stopped around 9ft to cool down, just stayed there and shot a doe at 22 yrds about hour after daylight.
I think most people stay around 15 feet. But I suppose there really isn't a "lowest". But the lower you go, there is a greaterrisk of getting busted (i.e. movement, scent).Like Hiawatha said, "rule of thumb around 15 ft".
If you think thats to high, then go up where you are comfortable and start from there.
Goodluck!
Crutch