IF you are truly ONLY 15, then let me say YOU are well on your way to achieving a good and faithful understanding of the Word of God, and good for you!
As for water baptism, it is not necessary for salvation, and you are correct in that there are times when a new believer can not be water baptized, but they will still receive their reward, times such as a "death bed or battlefield" conversion. However, do not lose sight of the fact that water baptism is important for all new believers to do because there is a reason. If you reread the OP, you will see the reason(s) I discussed.
God bless, and hold strong to the Faith.