You know, I was playing around with the "card system" as I've come to call it, and decided that I like the idea, but for my table I added a bit to it.Ignoring that I am also working within a 6-15 range - which one could readily expand to 3-18 - I think draw without replacement has a lot to commend it. I prefer it to setting bounds for keepable characters... although right now I can't quite articulate why. Maybe because if the intent is to bound, I prefer a design that produces values falling within the bounds?
After you have determined your ability scores, you can add 3 points to one score, 2 points to another, and 1 point to a third. There are no racial adjustments.
I like this because it allows the player to shore up a weakness, enhance a strength, or balance things out to help favor a class they might want. Also, by removing the racial adjustments, it isn't an overwhelming increase.