It's his commission and processing fee (for arranging delivery to the clearing aagency etc). The structure is that you are registered on the exchanges through the broker. Different stock brokers have different schemes. Some like your broker seem to have flat Rs.15/=. Some other have charges as a percentage of value - between 0.25% and 0.50%. It's all legal and within limits.
Important points to note:
(1) The broker who is called as a trading member should have registered you with the exchange.
(2) For every trade done for you (even if done by you on your computer, it is through the broker's portal) you should get a mail from the broker with the unique transaction id which can be verified directly with the exchange.
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All other stock brokers are charging this, the same amount? I am from India.
