BB shoves 15bb into 20bb

Heads-up River | BTN vs BB | 100bb effective | Difficulty: Beginner

Hero hand

A♦A♥

Board

K♣7♣2♦4♠9♥

Action so far:
Pot 20bb on river K♣7♣2♦4♠9♥
BB shoves 15bb into 20bb

Pot: 20bb   To call: 15bb

Villain range: KK,77,22,99,44,Tc9c,8c6c,bluffs (busted draws)

Your move: