Many Lego Blocks - InstancedMesh Performance


I’m attempting to create scene a faux lego blocks scene with 360+ groups of 48 x 27 individual lego blocks.
I tried with a single InstanceMesh then settled with one per group with 1297 blocks in each. 466,560 lego blocks in total.
All positions and colours are set with a matrix and do not change, only a tweened camera, but performance is slow. No textures.

I was hoping that culling would reduce the impact of the high number of blocks, but this is not the case.
Can you advise a better way of dealing with this / approach please? Please see the first method renderCertifications in the codepen below to see how I add the meshes. Any insight into improving performance would be greatly welcomed.