The best way to speed up responses is to use a lesser model (eg ADA and Babbage)
The API takes time to come up with its responses. The better and bigger models have larger latency.
Some more complex responses have been know to take 10 or more seconds
However, the smaller models may not have the knowledge or be as capable/accurate at your task
ADA is really good for classification promtps - but not so good at factual writing