Just looking at the cover, it is a full-screen image inside a PDF. The text isn't crisp even at 100%, and if I pinch and zoom the page the text isn't resolving into a high-quality version. The same is true for every ad page. It isn't until I get to the editorial content where I see truly vector content.
The pages that are full-page images and then made into PDF articles are why you are having memory problems. I'm not sure what your production process is, but for those articles you are better off setting those articles to be PNG format instead of PDF (you can mix both article types within the same folio).
Neil