Its all configurable. The latency of the connection depends on how often device sends advertisements on one side and scans on the other. For example if both sides know that connection needs to be established and sends advertisement every 20 msec and scan all the time, the latency would be around 20 msec. But that would eat too much of the battery. There is some discussion about that in the How to Write Application document. Very similar for the data, disconnection there is a connection inteval. If this is set to minimum (7.5 msec) the latency will be short. But that would take too much of the energy. So connection iterval is is set based on the latency requirements of the application.
