I did this scene last night. Rendering with Cycles (time: 1 hour approximately).
Walnut have 4 displace modifier and a texture mapping.
I hope you like it
Really nice renders Great Job!
I think that the walnuts are non done well
I suppose the walnuts aren’t sculpted and you applied a mapping for the texture to recreate the creases and other bumps. The walnuts might need a multires surface to receive more detail input from the texture mapping, but that’s just my humble suggestion. Otherwise, the walnuts looks a little too “plain” for a close up.