Card game: pick cards that sum to 15

You get a small existing codebase for a card game played with a 36-card deck, and you may use an AI assistant. The game revolves around picking cards whose values add up to 15 (the common version asks for three cards).

1. Find and fix the bug that makes the provided tests fail.
2. Implement the function that finds cards adding up to 15 among the cards available.
3. Make it faster, then improve the playing strategy so it scores as many points as possible over a game, and explain how you evaluated it.