Your penis and testicles don't stop growing until you do which is around 21, I'm 17 and I can tell you the size has changed quite a bit since 14-15 even 16 years old.
One tip: after you pee, or even in the shower, or in your room when you have privacy, shake and stretch it around, don't do it to the point where it hurts but this is suppose to make it bigger over time, not longer though, just thicker, wider, fatter what ever you want to call it.
Also making your penis semi-erect, so when it's in the middle of getting erect, make a ring around it with your fingers and squeeze up it makes the head bigger over time (from my experience) and when erect put your penis through a full toilet paper roll and try to hold it up as long as you can this stregthens the muscles around the area and makes it bigger slightly.
For acne, I had tons as well it's almost gone now. It's just a phase your body goes through. try drinking green tea everyday, that helped mine.