Below 24 will seem laggy. It requires 24 frames to trick the human eye into thinking stuff is smooth. Humans see in 30 frames per second, and 60-80 in times of frustration, like in war, thats why soldiers say "It happened in slow motion", because the brain makes the eye pump out more frames, making vision slower, and smoother.
I believe I am correct on my figures, correct me if I am wrong, I'd like to know.