Any graphics, ANY ANIMATIONS, and ANY sounds will slow down PowerPoint, no matter what platform you're running it on. Worse, too many bells and whistles confuse PowerPoint and make the presentation either stop or not work as expected. Maybe "you'll embarrass yourself AND the department when this finally does happen to you" can help convince your users that "simple is better." It's obvious that "getting to the point" is beyond them, or they wouldn't have 80MB presentations to begin with.
Yeah, I'm grumpy about it, but PP is so easy to use for "good" presentations that it's easy to abuse for "not-good" presentations. Most people should be forbidden from creating their own presentations from scratch because they can't see the "forest" of an overall impression for the "trees" of their pretty, shiny, annoying embellishments. Instead of coming up with something that looks professional and gets the point across, they come up with something no self respecting third grader would submit for grading. But it's "professional" because they used a computer to make it... Sigh.