Plus, with 15 digits of precision you can measure the the distance from the sun to the Earth in millimeters. You don't really need it.

Any observation or measurement is limited by the least precise component - in physics things are measured accurately out to about 7 digits of precision or so. Since you don't commonly use trig on currency operations - what are you trying to do -- that requires more than 15? Calculate the diameter of the Universe to a micron?