Well, It depends upon various factors. Frame rate drop is not only associated with draw call… There are various other factors that involves in frame rate drop.
If you have created a script which involves inefficient and lot of memory consuming scripts, which eats lot of memory and it will be also an cause for the frame drop.
You can find below the link for efficient game build… it is quiet harder to address the exact thing which pulls down the frame rate as you have not mentioned clearly the poly count, Texture information etc.
There are a lot of things to consider. It could be a shader, or it could be a script that keeps trying to find a gameobject in Update. (just an example)