In tools like postman, u have to prepare the entire request (url, headers, payload, etc) and then execute it. And, in soapui too, first you will prepare the request though soapui generates a pre-populated envelope where you have to only supply the values. Once the request (url, payload, etc) is ready then you will hit the request. And, you get raw xml response which is not processed further.
In the soap snap, once you hit the execute button, it doesn't directly hit the endpoint. It has to do some preprocessing (check if there are any placeholder values in the envelope to replace them with the values from the output of previous snap, remove empty elements from the envelope, etc). Once the enveloped is evaluated and optimised then it hits the endpoint. And, once the raw xml response is received, the snap will then process the response to convert into a snaplogic document so the next snap can consume this output.
Due to the pre and post processing involved in the snap, the response time for the execution of the snap could be slightly more than that of postman, soapui, etc.
HTH. BTW, can you tell how much difference you see in the execution time of the snap vs soapui?
