I'm just guessing, but if you export h264 (becomes mp4 ), it is pretty high compression. If you choose export at 720p instead of 'source' ( assuming that is 1080p) -- which means you are down-scaling it -- then you will get a pretty low res small byte count file to just look at. I would keep the bit rate at the default settings and don't choose any other things ( max bit depth, or whatever you see down on bottom of choices. just leave it alone)
See if that does the trick.
Otherwise you have to go down scale MORE and keep it progressive or whatever, and then it's custom settings all the way.
what you mean to say, instead of "raw, so to speak" is misleading and is the wrong word. What you mean is like 1/4 resolution in preview and just a 'fast down and dirty export' so you can look at it over time and decide how to adjust your editing and tell your story.
Nothing wrong with down-scaling and compressing to "view" .. and is smart. So go for it !
Good luck !