Large simple ground/floor object killing android FPS

So I’m making an android VR game - to run on Pico - and what i’m finding is that it’s dropping 20fps just for the adding of one large flat ground plane. The plane is 50x50 units/meters and is using the standard shader with NO texture on it…
This is a basic (i guess) optimisation question but i can’t understand why that one object is costing so many frames.
I’ve got a load of other normal objects in the scene - low poly trees etc and they’re all fine… but for some reason - this non-shadow-casting flat plane without many polys kills the frame rate…
Anybody want to fill me in on what i’m missing and how you go about ground/floor planes on mobile… Thanks!

Have you tried Occlusion culling?

Did you try to swap to another default shader to see, if this might be the problem? Also, what @ddulshan means is, try to split your floor up into multiple tiles so occlusion culling just renders the needed parts and not the whole huge plane. Anyhow, I am guessing the shader is doing some weird stuff.

Mm actually I worked this out now… the big floor plane had baked shadows on it… and this shadow map, in order to have nice resolution up close, was too big or something i think. When i remove the baked shadows this works… or if i subdivide the plane up it also works (smaller multiple baked shadowmaps.)
Boom.