Powerpoint is well-known for excessive filesizes of presentations.
To break it up is straightforward. Take a guess how many slides you need in each of the broken-up separate files, they are likely pretty much of a constant size if there aren't any embedded videos in there. Copy the original first, of course, so you don't lose it, then create one (or more) new ones (File-New-Blank Presentation), and save with names. In the copy, in the thumbnails down the left side just click one, then hold CTRL down and click some more until you have what you want. Right-click over them, select Cut, go to the new presentation, position over the first blank thumbnail, right click over it, and paste. You can just take time over this until everything is split up as you want it.
Winzip is not particularly efficient with photographs, there's not a lot to compress.