Fran,
The Velop system can manage multiple users and keep the speeds consistent, however, like with any other wifi system and internet data stream, it will all depend on the bandwidth of your service. If you only have 20 Mbps, using the Velop system can only use this bandwidth among the 15 people. The Tri-mode system of the Velop helps ensure that maximum speed is available for the bandwidth you send it.
In short... all systems will eventually slowdown as the demand increases. This system attempts to maximize what it is given.