Most efficient (less lag) side scrolling level?

Hi!
Recently I start a little and easy project that is some kind of side scrolling where you just pick up stuff and avoid obstacles, I already add all the physics and stuff i wanted on the player (that only moves up and down and the background is what moves toward it)

When I face the level construction I thought two ways:

1- Make a one big movie clip that include all the map and make it move using
“This._x -=10”
Its easier but i think this may generate too much lag, and the level size will be limited to the work-zone size

2- Make a “Level controller” symbol that contain a time line that at specific amount of seconds load each the obstacle movie clip to the scene (a little outside of the window)
And exporting each obstacle kind to AS and add the code:

this.onEnterFrame = function() {
    this._x -= 10;
    
    if (this._x< -200) {
        this.removeMovieClip();
    }
};

in the obstacle’s frame.

Removing them when they are outside i think it will reduce the lag

I wanted to ask if anyone knows a Most efficient (less laggy) way to do this…
I’ve heard about the array method but im not really sure of how is done… and honestly dont know if worth to use it on something as simple as this…

Opinion, suggestions?
Thanks.