The .NET webservice for sending and receiving TMA transactions replaces the BPEL webservice originally distributed when Exor TMA was first developed. It was introduced in TMA 04.07.00.00 fix 8.
The .NET webservice is set up so that during 'quiet' periods, the polling for new transactions slows down to 15 minutes to save resources. Once it finds a new transaction, the polling will speed up again. So you will often find the first transactions in the morning take 15 minutes but thereafter they will send much faster.