What is the average Byes for the losses of 15, and before 1874?
CREATE TABLE "2007_ladder" (
  "ballarat_fl" text,
  "wins" real,
  "byes" real,
  "losses" real,
  "draws" real,
  "against" real
);
SELECT AVG("byes") FROM "2007_ladder" WHERE "losses"=15 AND "against"<1874;