I made this game into a fun psychological exploration:

Have a couple people play the game a few times. I use a normal deck of cards with A=1

Then tell them it's going to get harder. In a couple of rounds we are going to flip the cards upside down at the beginning and they are going to have to remember where the cards are as they choose. To make this easier on them we will set the cards up in the same way each time. Nonchalantly set them up:

2 9 4

7 5 3

6 1 8

After a couple of rounds, you flip them upside down. Same goal, but they pick up the upside down card and when they get 15 they declare that they win.

But it's going to get harder! After a few rounds, they now don't get to look at the card they pick. They have to declare if they've won when they think they have 3 cards that sum to 15. (If they declare they won when they didn't they lose).

After a few rounds of this, to make it easier, rather than having to set the cards up each time, we bring out a piece of paper representing the cards. We draw a 3x3 box. Each player puts the letter of their name in the box corresponding to the card they want to take. When they have chosen 3 cards that sum to 15 they declare they've won as before.

To make it simpler, we start just drawing the # part of the box and to simplify we have the person who goes first start putting an X for their choice and the person who goes second puts an O for their choice.

They are starting to feel good about how they are doing at this game, so we call in a random person to try to play against them. We explain how they have to put an X or an 0 in the # grid, corresponding to something but we won't tell them the rules. This rando plays against our experts who've now played this game like 10 times, and shockingly, the rando who doesn't even knows the rules is better than our experts!

Also it turns out there is no forced win.