Unity UI Low performance in a heavy UI game

I'm trying to locate and fix the reason our game is performing poorly, specifically on mobile devices.
Using the Unity Profiler it seems that the biggest portion of computation goes to EventSystem.RaycastAll & Camera.Render (drawing/culling).
This is not surprising since our game consists only from UI elements, but at least it shows that our code is not causing huge performance hit.

Because only UI elements are present many sources I found on the web to improve performance are not of much use. These links, however, seems to have the same problem our game suffers from
https://forum.unity3d.com/threads/how-to-reduce-cpu-usage-when-not-doing-much.343216/
https://forum.unity3d.com/threads/event-system-performance-pretty-bad.292570/

I tried removing excess GraphicRaycaster from various UI elements but it didn't seem to help since no matter how I turn it, the game is made from UI elements and require the raycaster to interact with them.

Is there anything else I can do to improve the game performance?

 

Are your elements using sprite atlases? How many draw calls?

 

Are you disabling game objects that are not visible? I mean closed panels?
Here is the asset that may help you! It's called Woo Panels. It is highly optimized and it was used to make UI heavy MMORPG Maguss. Here is the forum thread.