No one can be sponsored by a family friend. A U.S. Citizen can sponsor their parents, siblings and children. If someone came into the U.S. illegally, they may not adjust their status in the U.S. under most circumstances. If the child is under 18 and has been abandoned, abused, or neglected by his parents, there may be a way to adjust his status.
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Andre Olivie, Esq.
I agree with the above answer.
However, a 15-year-old child cannot accumulate "unlawful presence" in the U.S. You should consider any method by which he /she can acquire lawful permanent residence in the U.S.