Select as many objects as you like and let Instances To VRay Proxy find any instanced objects and convert those instances to VRay Proxies.
But high poly object, intended for intensive instancing is the cause of prepairing objects phase.
I'm a little confused, My trees are really high polys, and theirs a lot of instances.
This may sound difficult but Instances To VRay Proxy will optimize your scene to do faster renderings and all you have to do is pick an output path and hit a button!
Instanced VRay Proxies only need to be loaded once per proxy mesh.
It lets you reduce your rendering times and makes final rendering and preview rendering dramatically faster compared to the standard rendering process. Free trial available by clicking green TRY button above !