If you think the machines in the lab are rendering slowly, look at the task manager. You will see that Metal Ray is only using about a maximum of 25&perc; of the power: two out of four CPU cores
Googled for a solution, found one on Creative Cow: Go to the Batch Render Options (hit the box) and under Parallellism, turn off Auto Render Threads and set Render Threads to 8. Turning off Render on network machines may also be needed.
Happy Rendering