Hi,
I don't believe that SoapUI would cache the results, but your backend might.
I don't have a solution, but I have seen similar behaviour from an API that has to go to a db for results. I found the first call was slower than subsequent calls and this is down to the db caching results. Therefore, when running any sort of performance tests, I would call the API three times and report each result to give min, max and average.
Back to SoapUI, are you measuring the time for the test as a whole or purely the step to call the API?
