I have a video I made in Premiere Pro that is like slides with 150MB audio. How can I export it to a reasonable size?
Without knowing either the resolution or the duration of the video is hard to know if that is a good file size or not. But in any case, you need to define a CODEC and a container for your video. And define the resolution of the project.

A typical one is FULL HD (1920x1080px) and the most used container is Mp4 with an h264 and ACC codecs for video and audio.

You could totally lower your framerate to even 1 pers second if you have direct cuts in between slides, but if the video has transitions between the slides you can not. Use 24Fps.



Of course, you already did your work, next time you can actually do it in a presentation program, and export it from there.