The system only checks for collisions when it's needed - if you have events "On collision" or "Is overlapping" or if there are behaviors on the objects that register collisions (platform, physics etc.)
So normally your destroyables should not generate collisions check with the walls.
You said your layout is (1400,800) - is this in pixels or is this the number of tiles on the tilemap?
If in pixels, it's not that big and you should be able to use tilemap or even several tilemaps on top of each other.
If you have lots of individual sprites like destroyables, you can disable/enable collision for them if they are too far from the character or in another room etc.
System-> Pick by comparison-> Sprite where distance(Sprite.X, Sprite.Y, Character.X, Character.Y)<100 : Sprite Set collision enabled
System-> Pick by comparison-> Sprite where distance(Sprite.X, Sprite.Y, Character.X, Character.Y)>=100 : Sprite Set collision disabled