It really depends on what you want.
I can guarantee that people who have the money, a nice entertainment center, and a good movie watching enviroment will buy 15+.
People with the modern television, and nothing special will probably go with about 15, give or take.
I own about 20, recently been buying more classics for 10 bucks. Renting is usually my preference, if its good Ill purchase. If its just a one time deal, I wont.