If you're looking for a 15/64 drill bit, the good news is that it's a fairly common size. The bad news is that there is no standardization among manufacturers when it comes to sizing drill bits. As a result, a 15/64 drill bit from one manufacturer might not be exactly the same size as a 15/64 drill bit from another manufacturer.
That said, most 15/64 drill bits will have a diameter of just under 1/4 inch (slightly less than 6.35 mm). They'll also usually have a flute length (the part of the bit that actually does the drilling) of around 2-1/2 inches (63.5 mm).
When shopping for a 15/64 drill bit, it's important to pay attention to both the diameter and the flute length to make sure you're getting a bit that will fit your needs. With so many different sizes and styles available, it's easy to find the perfect 15/64 drill bit for your next project.