So sorry, I didn't know the dimension of your project. I have no clue about how you can solve your problem.
Maybe doing smaller maps, where the amount downloaded for each layout is minor.
I have read an article a time ago about how the downloads works too, and there they explained the wast of bandwidth when the user need to download all the project in one single shot.
By now, it's nice, because C2 have a feature to download only the necessary for each layout, and doing smaller layouts, you can guarantee to the player a fast download (using a custom loading screen for the transitions, where on a fast server would be imperceptible) and if the player don't finish the game, you'll not waste the entire game size on a single download.