In the case of my current problem, I have a high band-width.
I saw that fop.jar is 1.6Mo, it should need Xalan and Xerces too, so between 2 and 3 Mo. (I don't use SVG, so I save 2Mo of Batik)
This is not the problem in my case.
Embeding FOP in an applet would make your applet humongous. It would only be possible in a LAN configuration with high band-width.