Q: I made a video on an iPhone 5 se and it plays back in high speed?

did you make a time lapse video?

Hi

You recorded your video using Time-Lapse mode. It is not possible to slow this down after having recorded it via that mode.

More information:

http://help.apple.com/iphone/9/#/iph1e767793c

Note that Time-Lapse involves taking a series of photos that are compiled into a short, high speed video, so is different than continuous footage being played quickly vs slowly. The mode is intended, for example, for capturing events such as a flower opening over a period of time.

If you edit the movie to slow down the speed (for example, by using iMovie on a Mac), then, when playing it back and depending on the footage that you captured, the result may be jerky movement, as the video moves from one photo to the next. 

You're welcome!