What is the ruling on delivering lectures and speeches after the obligatory prayers in the mosque when I am 15 years old?

It is more befitting for young people to strive in acquiring Islamic knowledge before presenting themselves for teaching, based on the saying of Umar, may Allah be pleased with him: "Gain understanding before you lead," and the saying of Al-Shafi'i: "If a young person presents himself for leadership, he misses out on much knowledge." If scholars approve the student and deem him qualified for narrating and teaching, then let him disseminate what he has learned with sincere intention. There is no harm in delivering speeches and admonitions for practice, provided that he verifies what he delivers and does so under the supervision of someone older and more experienced.