You got another 15 rep because your answer was accepted. See https://askubuntu.com/help/whats-reputation for details about reputation. The relevant bit here is:

You gain reputation when:

 

[ . . . ]

 

answer is marked “accepted”: +15 (+2 to acceptor)

You got another 15 rep because your answer was accepted. See https://askubuntu.com/help/whats-reputation for details about reputation. The relevant bit here is:

You gain reputation when:

[ . . . ]

answer is marked “accepted”: +15 (+2 to acceptor)