How long do trailers and commercials last before the actual movie starts?

Right now, after the lights go down, Cinemark shows 15 minutes worth of trailers before the actual movie begins while Regal’s trailer block runs 15 to 20 minutes, according to the news report.

https://entertainment.slashdot.org/story/19/10/01/1634225/movie-theaters-latest-gamble-ads-mixed-in-with-trailers