By reference objects you mean that option when using Duplicate Special, to create references of the same object ?
No i mean you can create a low resolution version for your scene as a proxy then in Mental ray you can reference the high res geometry to come in at render time.
Here is a tut that might help you https://www.antoniobosi.com/maya-tuto...oxies-tutorial
Also as another option you can set your models to display as bounding boxes or duplicate them then put them on their own layer and actually convert to bounding boxes Modify > Convert > Geometry to Bounding Boxes.Don't forget to hide the high res geo on a layer.
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