I see these are XML files of about 120MB in size. Zipping them only reduced them to 42MB so you are asking for far more which would mean you would strip out all the XML leaving only the data leaving it to not be a KML file and still far from your 5MB size.
What you could do is to edit the file to 5MB files but since I don't know all the reasons for your call here, I can't offer other ideas other than no, you won't be doing this.
Hello! I am trying to create a KML/KMZ of the boundaries of the National Parks which is smaller than 5MB. I have downloaded the giant files from their website (see below), but can't compress them enough. Does anyone know of a way to make this happen? If you open the NPS URL, you can download the files in the middle right of the screen. I don't need crazy accuracy.
Steps I've tried:
1. Save KML in comressed folder (i.e. create KMZ)
2. Put KML into Google Earth and save as KMZ
3. Reduce precision from 8 decimals to 5 decimals (see URL below)