David Arnold (prof at SOAS) suggests 40m died from cholera just in India from 1817 through 1950. ( http://www.amazon.com/Colonizing-Body-Medicine-Epidemic-Nineteenth-Century/dp/0520082958 ). 15m of those prior to 1867. So the number doesn't seem too unacceptable as a guesstimate for worldwide.
Wiki is definitely shy a few numbers - eg 1866/7 seems to be missing figures for places like Britain and Prussia.