What is the Set 3 with a Set 2 with 15–6?
CREATE TABLE "pool_b" (
  "date" text,
  "score" text,
  "set_1" text,
  "set_2" text,
  "set_3" text,
  "total" text
);
SELECT "set_3" FROM "pool_b" WHERE "set_2"='15–6';