How do I make the closed caption stay on screen longer

Sure. Adding a bit of silence lengthens the audio. That would let you lengthen the caption duration, so folks would have a bit more time to read it. 

The best way to ensure that everyone has the time they need is to include the video controls, which let them start and stop as needed. (I realize that also allows someone to skip to the end. But the controls could be covered until after the video plays completely the first time.)

Another option would be to include the transcript in the Notes, or perhaps on a layer. Those aren't good options if the audio is describing something being shown in the video. But they'd work for general narration.