Packet sending latency is highly dependent upon the protocol and transport. E.g. for MQTT QoS 0, the packet sending latency will be lower, as the transmission of the packet is marked completed almost immediately. If the QoS value used is 1 or 2, the sending latency will be much higher for the same test, as higher QoS values require every sent message to be acknowledged for delivery, therefore considerably increasing the latency.