What is the Sharia ruling regarding sexual intercourse with a child by a 15-year-old?

If adultery is proven against a person, the ruler must carry out the prescribed punishment on him (stoning for the married person and lashing for the unmarried). As for the person himself, he must offer sincere repentance by abandoning the sin, regretting it, and resolving not to return to it, and by increasing good deeds. He must also conceal his sin, based on the Prophet's (peace be upon him) saying: "O people, it is time for you to desist from violating Allah's limits. Whoever commits any of these abominations, let him conceal himself with Allah's concealment, for whoever exposes himself to us, we will apply Allah's كتاب [law/judgment] against him."