Considering that it’s over 70%+ of phones that have NavigationBar there is something you have not thought of.
As you can see, I’m unable to see your Ad-Banner.
Reducing even more memory is to use one image and not two as you do it right now, just for fun I have made a replica of your app just to show you how you can do this.
Btw, I will send it to you as soon as I get home…