Hello
This is actually expected, when you run a loadtest the response time is expected to be higher, it depends on how much load the server is taking and how powerfull it is, but also notice this is an average, not the time for each en everysingle vuser, so let say you ran 10 vusers, and all of them nedeed 2 seconds to complete this transaction, but 2 of them needed 10 seconds and one more needed 20 seconds, so the reported average will be 5.4 seconds, the less vusers you run the higher the impact in average, you should check the 90 percentile to get a better idea of what is going on with most of vusers.
hope this helps
regards