Fonts, especially decorative, have to render on the screen. This makes it hard on the Flash player.
There are a few ways to eliminate this problem:
1) Click your text and set it to "Anti-Alias for animation" in the Properties panel. This will degrade the quality of aliasing (you know, the semi-transparent pixels that smooth the edges of fonts?), and will make the fonts happier. Or you can set the Aliasing settings to as low as you want, just keep playing with different options.
2) Break your text. Sometimes (okay, rarely) Flash runs text faster if it gets broken down into vector. Ctrl-B your fonts a couple times and see if vectorizing them helps.
3) Use a simpler font, or less of it at a time. Yeah, it sucks, but Flash is not that powerful, and moving complex fonts around hurts its head sometimes.
4) Convert to bitmaps. Convert into png-24 files in Photoshop then move the text over, see how that treats you. Bitmaps are to eating a big piece of steak as fonts/vectors are to eating sushi... a lot more filesize but a lot easier to get in your mouth.