First obvious question: why? I did these for the Reddit forum /r/FullMovieGifs. Why do (some) people like them? Because it gives a nice feeling to be quickly reminded of a favourite movie, and also it can reveal things not obvious in the full movie. For example, Paul Thomas Anderson likes really long takes where the camera slowly, slowly zooms in; this is way more evident when you watch the gif of Magnolia, below.
This was not just a matter of taking one frame every 10-15 seconds; I did my best to choose specific frames in order to give the best possible summary. I tried to linger on the most important and/or memorable scenes, and go quickly through ones that were less important or were a wasted frame (such as most establishing shots, where they show the building exterior before they show the characters in a room in a building; it's a good visual shorthand but useless in a gif), or were disorienting (long dialogue scenes that flip quickly back and forth between two people's faces are way more kinetic and disorienting in gif form, so they had to be cut down and the frames carefully chosen.
Here's an example of the frame rate of the Star Wars, Ep. IV (which I call Star Wars, 1977 above, 'cause I'm old and stubborn). You can see it's not very uniform, and if you click to enlarge you'll see I lingered on the most iconic scenes.