I had a similar problem. An action set up with maybe 200 layers, all with quite expensive elements, previewed in realtime fine. Very basic rendering came in at hours!
Colour correcting/blurring in Action causes it to load each frame element (render the blur etc) and then rasterize it before putting it in the scene; it does this per frame. Ouch. 200 CC’ed elements later…..
I also get the feeling that in Batch it works on a matte output even if it doesn’t get used.
Ant