This level is very hard to complete. To get 3 stars, you should pop all pigs and score 72,000 points. The important shots is snipe kernels with Lazer Bird to make towers unstable and blocks destroy popcorn as much as possible.
For Utopia 4-15, fling the Ice bird into the pile of popcorn kernels on the candy apple planet, pushing the pig northward into the TNT. Then loop the Lazer bird around the southern side of the apple planet, waiting for it to approach the edge of the playing area, then redirecting it into the pile of popcorn kernels on the eastern side of the main planet.