I don’t understand your question.
Are you transferring the call using the Transfer button or softkey on your phone? If so, pressing Cancel should get you back to the original caller immediately.
If your device doesn’t have a built-in transfer function and you are using *2 to do an attended transfer, then pressing *1 during the busy tone should get you back to the original caller immediately.
The situation seems unusual in the first place – call waiting, voicemail and follow-me are all disabled?
If the above is not useful, please describe the exact actions you are taking and what goes wrong.
(If you want to change the 15 second timeout, see Attended transfer timeout , but note that this timeout also applies to no-answer, so it’s not a good idea to make it too short.)