Rendering isn't a problem, but active object count can still be an issue if you have loads of stuff going on.
Often my projects end up being loaded with crazy amounts of moving and complex math with the visible objects, and so anything that the player can't see is often destroyed or majorly simplified in it's calculations in order to save processor time.
Ultimately, you need to just make sure you aren't making images that are too big... OR making too many objects in total that are moving or have some "every tick" math tied to them (like loops every tick, or tracking coordinates, etc).
Having a single large picture is the big killer though, especially when it comes to mobile platforms. I would recommend to keep you images to as small of a size as feasible, especially if you have a lot of repeating or re-used imagery. If your map has a road on it for example, you can make a few road tiles and create every length of road from 4-5 small images, rather that having a giant image of a road for example.
Hopefully this will help.
What I meant by making tiles isn't necessarily making a "tilemap" - just cut the map into smaller pieces and still use them as sprites if you want. I often make my own "tile map" by using a loop to place sprites all over the layout as the "tiles" so I can still use collision polygons, image points, and all that stuff. Again, there is a balance point between having too big of an image, and too many objects!