Want it to rain icons - slowly

I am working on a project where I want a dozen or so icons to fall slowly from the top of the screen to the bottom.  I placed the icons at the bottom of the screen and applied a "Fly-In" animation set to "Very Slowly."  This looks beautiful in preview, but when I publish, the icons go too fast.  I've tried extending the timeline, but it only helped a bit (and I cannot make it any longer).

I also tried creating the animation in PowerPoint, and saving as a video.  The problem with this is that the video looks choppy (of course it is not choppy in it's original form, and also looks great in Preview!).

 Does anyone have any ideas how I can make this work? 

Thanks in advance for your ideas,

Jill