High quality render crash

Used 285 mb
Free 5309 mb
Scene verts 578k

The model vs my ram feels adequate to render out 4k… I have 4 lights and have several post processing effects. The best I can do without a crash is 1750 x1750 square.
I joined all layers… do I still lack the ram for these post processing effects? Subsurface, ambient occlusion, tone mapping, color grading. Only used vertex colors, no textures…

I closed all other apps and used device care to enable ram plus bumping it to the max 8gb

Samsung galaxy tab s7