I have some reserved cards in Splendor and 15 prestige points at the end of my turn. Is this the final round of the game, or do I have to buy all my reserved cards to end the game? Do reserved cards have some "negative" points assigned to them for points counting?
Reserved cards have no effect on the end game trigger, and do not count as negative points. The rules just say that "When a player reaches 15 prestige points, complete the current round so that each player has played the same number of turns. The player who then has the highest number of prestige points is declared the winner".
Not officially, but it is a common house rule I have run into, among a few groups of players, that you have to have 15+ points but reserve cards count as -3 each.
So you could go out with 18 points and a reserve card, but your score is 15. Likewise if you have 15 points and a reserve card, you need to get rid of it, or get 3 more points to close it out.