i am 14 years old and my dic@ is 15cm is it good size?!

There really ISN'T an average penis size for a 14 year old, because no one goes around asking 14 year olds how big they are. See the chart at the link below for the average size of an ADULT penis. According to the chart, you're on the high side of average for an adult male (15cm / 2.54 = 5.9 inches - GAWD, I HATE METRIC, NEXT TIME MEASURE IN INCHES...PLEASE!), and since you're only 14 you may have a little growing yet to do.
Regardless, there's nothing you can do to make it any bigger anyway. It's all controlled by genetics. You may end up being 6" or 6.5" or 7"...who knows. Either way, just be happy with whatever you have. Having a big penis does not make you a better man or a better lover, knowing how to do all the "OTHER THINGS" for a girl (kissing, touching, rubbing, licking - in ALL THE RIGHT PLACES) is what will make you a better lover..and THOSE are things that you can do something about.

http://www.average-penis-size-chart.com/

Yes its the perfect size, smaller is below average and bigger it starts to get uncomfortable in the underwear region ;)

Yes your are over average for a grown adult

could you give us that in inches