This one can be obtained quickly.
- From the main menu select "NHL THREES"
- Then select "THREES NOW"
- Select the Eastern or Western Mascots team (by pressing down on LS 4-5 times) for the team you want to be; then press A a few times to advance the screen.
- You can customize ("STIPULATIONS and SELECT PLAYERS" tab) the rules and which mascots are on your team if you like (limited number of mascots are unlocked when you first start the game). I suggest you change the rules of the game to end by goal limit as opposed to time and set the goal limit to more than 5 to give you a little cushion.
- Select "ADVANCE" to start the game.
- During game play you control all 3 players on the team so just pass the puck to and only shoot with the mascot you want to score 5 goals with.
- Pretty easy to do... enjoy your 15G!
** FYI - there is an option for a "MONEY PUCK" while playing THREES. This will make some of your goals count as two or three goals as opposed to one. However, please note that you need to score 5 actual goals with the mascot, even if that means your team score is more than 5. My achievement unlocked when I was winning 6-0 because one of my goals counted for two points but I actually had to score 5 goals to get the achievement.
Please let me know if I can update/change this solution to make it better. Thanks!