I think the tile map object already works like this, as it allows you to create huge levels with small draw calls only rendering what is on the screen. For enemies you can just create spawn points in your level that spawn when a certain distance from screen and destroy after screen.
Otherwise the only way I can think of to do what you want is to use arrays to store your level tile positions and enemy positions and keep looking up the array to create tiles and enemies in the right position when the player is close.
But to do this you will first need to create a level editor to create your levels and enemy positions then store them to arrays and make code so your game can read the arrays produced by the editor.
Creating a level editor could, potentially, be more complex than creating the game itself, but it is a common thing to do and construct gives you nice form tools to use for such a thing.
as 
GenkiGenga said though run some tests with the tools that Construct 2 gives you first before you start thinking about other ways.