Separate components (and therefore Actors) are not intrinsically batched together in Unreal (for 2D or for 3D), so each individual component equals one (or more, if there are multiple material sections) draw calls when visible, and one item that has to be considered for culling. As I said earlier, you can see where things are falling down with commands like “stat game” and “stat scenerendering”, which will give you a better idea of where time is going right now.
Tile map components already (as of 4.7) batch together linear runs from same sprite sheet texture into one draw call, but always breaking between layers, so if your tiles are all in same texture page, a tile map will only cost one draw call per layer.
I have some plans to allow other forms of batching for 2D components, hopefully for 4.8, but nothing is set in stone. Current thinking is a 2D equivalent of InstancedStaticMeshComponent, and possibly a layer-based global batcher, but there are a lot more hurdles there.