For the same map there is a large difference in the draw call for the unity version 5.3.4 and 5.0.
I am attaching the screenshot.
Unity 5.0
The whole map is static. Shadows for directional light is disabled as well.
Because of this difference there is a fluctuation in fps as well.
Have you taken a detailed look using the Frame Debugger? (Unity - Manual: The Frame Debugger window)
One idea is that front-to-back sorting is increasing the number of draw calls to reduce pixel fill cost, but your frame is actually CPU-bound. In this case it might be better to turn off front-to-back sorting.
If you know your application is more CPU-bound, then turning this behaviour off might be useful, e.g. “Camera.main.opaqueSortMode = UnityEngine.Rendering.OpaqueSortMode.NoDistanceSort;”
Let me know if that helps.
