We currently have the video limit size at 200 MB, which is just under 2 minutes on an iPhone. Generally speaking, the best way to reduce the file size is to lower the resolution quality (you probably aren't going to need to watch these on a 1080 tv screen!). I've also noticed that mp4 files seem to take up much less size than mov files, so if they have a choice when saving, I would recommend that. 

They can also reduce the file size using QuickTime Player, which I believe most computers have by default these days. Under File/Export As... they can select the resolution that they want to export their file as, and that will affect the size.