Esther,
The above is good advice. I would also remove trash objects or shaders. Altho this usually only helps prevent errors when saving, but could reduce file size. Also Try it with multi-threading off (to check for a bug). That is rather large and from what I have seen toon rendering can take alot more time to render. I don't use toon pro tho.

No need to think outside the box....
    Just make it invisible.