Hi Haish,
I think all depends in the number of the common fields. You can provide a wsdl which paramerters could the type of call sales, inquiry and son on, then with these parameters you can filter the output. If you are talking about the same the same receiver endpoint, the same proxy or RFC, it is not a good idea to have 15 interfaces, however if you will have different proxies or RFC you should do 15 interfaces but all in the same Software Component because you are dealing with the same.
functionality.
Summing up, take into account the functionality and if you will have different endpoints or not.
Regards.