helena,
My 2-pennies worth:
Nicely organised event sheets I thought (I wish mine were that well laid out). There are too many collision checks and too many objects on the layout for optimum performance in mobiles (348 objects iaw debug and 648 collision checks per tick!!) - this is very high for any game like this, I think (I would strive for a max of about 100 or so for a mobile game). Your use of 9-patches doesn't allow you the option of enabling or disabling collision checks on them: if I were you I would use sprites of different sizes and to fit that job and then I suggest disabling collisions for those objects not on the screen - that'll save some processing power and might make it more playable on mobile/ipad. Seems a bit odd that you can check for a ball collision with a 9-patch object but you can't turn the 9-patch collision attribute off if it's off screen.
The backgrounds have collisions enabled which you can also switch off in the properties bar...
In my relatively limited experience of using C2 it is excellent for producing browser based games that will be played on a desktop or laptop computer. The android/ios export options are still embryonic and, although do-able for a Nexus 5, they don't work well on an 'average' phone: you will get much better performance from using another development engine if your primary aim is to deploy to mobile. But - and it's a big but - C2 is an excellent development tool. Depends on your intended market...