This Achievement unlocks at the end of the game if you get 15 three-pointers with one player.
Set up a game using a good team (like Florida) against a weak team (like Hartford) and crank the sliders up in your favour while reducing the sliders against the CPU. When you get possession of the ball, take all your shots from outside the three-point line (using the same player) until you get 15.
Increase the length of the halves from the pre-game options if you are having difficulty getting 15 before the end of the game. This is a good Achievement to earn while trying for the "100 Points" Achievement.