Any piece of software installed and running will have a certain performance impact. It is highly unlikely that OnGuard is slowing down systems because it is running. What might be is that if you limit network traffic before OnGuard has completed its scans, that application that cannot access network resources slow down the system.
Unless you are running on loaded old under-spec machines, I would not expect any slowness. You can try to run on an unprotected port, where no enforcement is done to see if that removes the slowness. If it does, you will need to find out what blocked traffic is causing the delays, and allow that if it is acceptable to security. Otherwise, please work with your partner or Aruba Support to investigate further, as there shouldn't be significant slowness.