In Acts 11, Peter is explaining the events that took place in chapter 10. If you would finish reading through verse 17, you would see they received the Holy Spirit WHEN they BELIEVED ON THE LORD JESUS CHRIST, not before they heard nothing at all. *Compare this with Acts 16:31, "BELIEVE ON THE LORD JESUS CHRIST AND YOU WILL BE SAVED." Acts 10:44 says, "THE HOLY SPIRIT CAME ON ALL WHO HEARD THE MESSAGE," not on all who heard nothing.
Acts 10:44 - While Peter was still speaking these words, the Holy Spirit fell upon all those who were listening to the message. "Began to speak" (Acts 11:15) and "still speaking" (Acts 10:44) are not in contradiction. Acts 10:44 says, while he was "still speaking," which means, he already started talking and said, "WHOSOEVER BELIEVES IN HIM SHALL RECEIVE REMISSION OF SINS" (Acts 10:43). So obviously, began to speak can't mean, said nothing at all yet, because that would contradict, "still speaking." There is a difference between "as" I began to speak and "before" I began to speak.