Try to use Vray to make grass. Use of Vray fur alone is cpu intensive. So use displacement and fur together. For instance if you have a 2d plane for the grass area then Add Vray Displacement Modifier and then Apply Grass Texture to the plane and add UVW mapping and Now add a subdivide modifier to the object and Add a Vray Fur object to the same 2d plane. I hope you will find this technique really helpful because, you get a sense of 3 dimension with vray displacement and adding minimal vray fur which sprouts out, it does look realistic and does not hog the rendering.