Optimizing enterframe code for multiple mc's

Hi, this is my first post so sorry if this was previously asked. I am calling duplicateMovieClip to create the enemies in my game. Problem is, I experience slowdown when I have many enemies in the game (not necessarily on-screen). They each basically do hitTests on enterframe to see if they are touching a wall, ground, hero, or bullet. So I was wondering if there is a better way to do this. Is there somewhere else I should be putting the code? I know some people throw all the code into one frame in _root and call attachMovieClip, but would that help me in my case? Any help is appreciated. Thanks.

edit: Hmm probably should’ve posted this in the game forum, sorry.