Hi!
I am also not circumcised, like 80% of the men on this planet. It seems like you are experiencing two minor issues. First you cannot fully retract. Don't worry this is very normal. When boys are born they are unable to retract their foreskin but as time passes the attachment between the foreskin and the glans of the penis is lost. Since you are 15 it is likely this attachment is likely lost (but not necessarily). So I think right now your foreskin is just tight. So to help loosen everything up I would encourage you to masturbate and pull/play with your foreskin. Actions like this, including sexual intercourse will help to loosen it up. You can also try one or both of the techniques below. You just need to be consistent with doing them. Your foreskin will not loosen up in a weeks time, but in a few months if you should start to notice that it becomes loose.
STRETCHING TECHNIQUE ONE
If the foreskin is very tight the simplest method is to pull back on the skin (easiest with an erection) so that the opening feels tight without real pain. Hold that for a few minutes and repeat a few times. Do this a couple of times a day. Soaking in a warm bath will make the skin easier to stretch. If the opening becomes sore, or develops splits, stop and let things heal up. Going at it too fast will only slow things down in the end.
Once the opening is big enough to just fit over the rim of the glans when erect the foreskin is at risk of getting stuck behind it. If this happens paraphimosis may develop. Stretching technique two avoids this risk
STRETCHING TECHNIQUE TWO
You can either grab each side of the foreskin opening (with the foreskin forward) and gently pull on each side of the opening or, even better, insert the ends of two fingers, even the little fingers and pull them gently apart. Stretch the opening in this way until it feels uncomfortably stretched but not actually painful. Hold and repeat as for method one. Once again this is best done after soaking in a warm bath.
You have what is called physiological phimosis (not pathological). Like I said earlier all boys have this and as time passes it goes away. Circumcision is not the answer. Physiological phimosis can always be treated without circumcision. If you live in the United States I would not go to a doctor because they have a circumcision bias. If you live in Europe, Australia and maybe even Canada you should be safe. A 6- to 8-week course of topical corticosteroids (eg, 0.1% triamcinolone topical cream), applied directly to the preputial outlet twice daily, can be tried to help speed up the process of stretching. However only try to get a prescription of this if after like 6 months you do not notice any improvements. You may also want to purchase this device to help with stretching. Though it is not needed.
Check out this link:
http://www.cfp.ca/content/53/3/445.full
Now for your second issue. Smegma does not cause infections. All it is dead skin cells, and natural oils. It helps your foreskin move across the glans more easily. At your age boys generally produce a lot of smegma but as time goes on you produce less. You might be producing a lot now because you are loosing that connection between the foreskin and the head of the penis. Do not wash your glans with soap. For some men this causes infection. Just rinsing the glans with water is enough to clean it.
Once again circumcision is not needed. Avoid it like the plague. Also check out cirp.org