I am a big proponent of believer's baptism, because I see it not only as a declaration of faith, but also as the same symbol of commitment as the marriage ring during marriage. That is a highly personal decision.
However, is 15 old enough? Depends on the person. I know that in Germany, the age of consent for religion matter is 14. However, I only woke up to spiritual matters in my early 20, so how about that.
Then there is the question of how his parents are with regards to him. Will they be merely annoyed if he got baptised, or will they be furious/violent/absuing or anything of the sort.
To be fair, maybe patience is order. We are not to be a stumbling block for others and we ought to obey parents whenever possible without going against God's will. Baptism is great, but I believe that it is not essential. Faith saves, not baptism. Maybe he can wait until he moves out or at least turns 18? You see, I would be inclined to believe that this is a lesson of God. It will show Jake that sometimes, patience is required and that the well-being of others at one's own expense is pleasing to God. 'Now!' is a very common attitude for youngsters, after all. And who knows, maybe he matures and finds out more things about hmself and God and decides to join a church that fits him better.