6/15 as a percentage is 40.00%. This is the rounded value you get when you express the fraction in percent form.
The fraction 6/15 can be reduced to 2/5, which represents the same part of a whole. Both forms show that a little less than half of something is being described.
In everyday terms, 40.00% could be the portion of a class that passed a test, the slice of a pizza you ate, or the amount of a budget that’s been spent. It’s a handy number to understand quickly.