IoT Core MQTT msg sending frequency difference between QoS0 and QoS1

Hello, I modified the sample program basicPubSub of aws-iot-device-sdk-python and try to send mqtt msg to Iot Core at 10Hz. Also I use AWS MQTT test client to subscribe and monitor the mqtt msg.
I didn't change the AWSIoTMQTTClient connection configuration and only change the QoS by the function myAWSIoTMQTTClient.publish(topic, messageJson, _qos). For _qoS=0, the sending loop time is about 0.1s and MQTT test client update the msg at about 10Hz. However, for _qos=1, the sending loop time become about 0.4~0.7s and MQTT test client update the msg at about 2Hz.

I wonder how to improve the QoS1 sending rate and what is the max frequency for it. Many thanks.

Below is my code for the main loop.

if args.mode == 'both' or args.mode == 'publish':
    message = {}
    message['message'] = args.message
    message['sequence'] = loopCount
    messageJson = json.dumps(message)
    myAWSIoTMQTTClient.publish(topic, messageJson, _qos)
    # if args.mode == 'publish':
    # print('Published topic %s: %s\n' % (topic, messageJson))
    loopCount += 1
toc = time.time()
t_interval = toc -tic
tic = toc
print('[%f]Published topic %s: %s\n' % (t_interval,topic, messageJson))
time.sleep(0.1)