My wisdom tooth is decayed and is it possible it makes my mouth smell?

Yes, but: There are many other possible causes as well. Even if you had a fresh smelling mouth, you need to repair or extract the wisdom tooth. Personally, i would care more about pain, swelling and spread of infection!

Yes: Yes, very likely. At your age, removal of wisdom teeth is much more complicated. Make sure you have the tooth removed by a board certified oral & maxillofacial surgeon.