What are the odds of making 15 foot putts?

every time i'm at the driving range i practice on the putting green after i hit a bucket of balls. i start putting 5 balls from 3 feet to 15 feet. at 15 feet, i usually make at least 1 in, and might make 2 or 3 in the hole from 15 feet. so are actually the odds of making 15 foot putts? and am i considered a good putter at this point?