Solution pH question?

It is bad chemistry to try and dilute a 15M solution directly to make a 0.001M solution. Particularly with a small final volume of 100ml. You end up with an unworkable result - having to use 0.0065ml of concentrated acid. You calculations are correct. You need to start with a 1M solution of HNO3 and even then you would need only 1ml stock solution. Or even better still 0.1M solution of HNO3, use 10ml diluted to 100ml. These standard solutions would be available in most labortaories.