Traffic shaping for video calling

Hi fgt ppl,

We have a video conference coming up and we need to minimize any lagging etc.

The wan connection we have is  20mbps, our initial plan is to use traffic shaping and set the guaranteed bandwidth to 15000 kbps for the one single internal IP address which is to used(for video conf equipment is my guess).

Will this gurantee 15mbps minimum for that one IP address while the rest of network gets whatever is left of it?

Is there any better way to do this?

Thanks