My webhosting:
We went through the log of sent messages. 1 message is sent in approx. 1s. If you include a delay, then the time will be extended. The server is able to handle many more messages in 1s, but the messages are not passed on (messages are sent in the given interval of 1s).
Try adjusting the setting to 180 messages in one minute without waiting between batches. It would be ideal to send parallel messages, ie to send several messages at the same time (eg 5 messages at the same time). Unfortunately, the module manual does not mention the option.