GR is not necessary for this type of renders, as others already said. GR computes light that bouces between objects in a scene. Here you have one model and a ground plane. Not much boncing light, but a lot of unnecessary computation. AO would be best here imho, because it would spread soft shadows around occluding surfaces, and and it would look quite good on the robe drapes of this Buddah. Be sure to use a lot of ambient light for the effect to be seen, otherwise, a lot of computation and no nice soft shadows.
Also if you are new to Vue, you may not know this, but you can cut rendering times greatly, by lowering the quality boost of the advanced lighting models to -1 in the atmosphere editor, without noticing any difference, most if the times.