If network congestion is high, you can limit the amount of multicast activity. If DAs have not already been deployed in the network, deploying DAs can drastically reduce the amount of SLP-related multicast.
However, even after DAs are deployed, multicast is still necessary for DA discovery. You can reduce the amount of multicast necessary for DA discovery by using the method that is described in How to Configure DA Discovery for Dial-up Networks. You can completely eliminate multicast for DA discovery by using the method that is described in Limiting UAs and SAs to Statically Configured DAs.