Movie previews, also known as trailers, vary in length depending on context:

• Individual preview length: Typically, a single movie preview lasts between 30 seconds to 2.5 minutes. Some trailers may be shorter (around 30 seconds) or longer (up to 5 minutes), depending on the movie's genre and marketing strategy

• Total preview time before a movie: When you go to a theater, you usually see multiple previews and advertisements before the main feature. The total time for all previews combined generally ranges from about 15 to 25 minutes, with many sources citing around 15 to 20 minutes as typical. This block includes trailers for upcoming films, ads for snacks, and theater announcements

• Variability: The length of previews can vary by theater chain, movie genre, time of year, and the specific movie being shown. For example, AMC theaters often have around 20 minutes of previews, which is slightly longer than average

In summary, while each preview is usually 1.5 to 2.5 minutes long, the full set of previews and ads before a movie typically lasts about 15 to 20 minutes in most theaters. This is why arriving exactly at the ticket time might mean you still have to wait through previews before the movie starts