I'm not sure about admob, but you can go through this list and see if any of it helps. It's something I borrowed from a thread to help me with my projects. It's pretty much a check list to help with efficiency. Just salvage what you can from it. I know the post was to someone else, but there might be something useful. Also someone else might be able to help better with your specific questions.
1.- for the red character: Use a container for the eyes
2.- for the red character: For the jump use image points or use EaseTween.
3.- For the whole project: use Powers of two in the sprites.
4.- Use PNG8 for the background
6. - Keep pixel rounding on.
7.- Don't play animations too often.
8. - Remove collision from backgroun images, and uncollidable objects.
9. - Pre-plan as much code as possible and use function object to cut back on events.
6.- Use delta time, you have lots of actions using time. That will help on frameratesss.
7.- Also, use Groups, your code needs it, a lot.
8.- And Functions, they can pass variables and data.
9.- And Families, you are using lots of single events for destroying any block. Example on how to fix this: Assign instance variable ID "destroyOnClick" to anything that you want to be destroyed on click, and create a Group for that.
10.- Why use WebGL if iOS doesn't support it?
11.- The code is ALL the time checking and updating the End Screen (just remove the forest background to see what I mean).
12.- Hide the End Screen btw., and only show it or create it when the red thing is over the Goal block.