Problem frozen app game android


I have created a simple game where we have a main character who is in charge of going through the scenes as long as he annihilates all the enemies. When this happens, taking the star reloads another stage with a different number of enemies. The issue is that when exporting to android, after overcoming several levels, that is, switching between scenes 10 or 20 times, the game starts to lag and eventually the game crashes. Because? I have the bullets with the behavior that they are destroyed when they leave the screen. Thank you.

I am testing with RAM memory usage in the mobile app, and I can see why the memory is growing form 66% to 90% and when arrive to 90% crash. Which event can produce to use Ram progresly?