Optimization of AndEngine game

I am using java + AndEngine in my game.

During the game i have some freezes, i looked for the information and found some steps how to optimize game performance:

1. Avoid GC (garbage collector) to be called in main action in the game:
   a)don't create objects while gaming;
   b)don't create unnecessary objects;
2. Optimize code that repeats very often

I followed these steps, but never the less i have some freezes during the gameplay.

Now i am creating and loading all of the textures before the game started and don't unload them, is it a bad idea ? How can i optimize the game proccess ? Maybe i have to make free all of the possible memory before main activity and then reload them after each level ?