What is the production code for episode 15 in season 3?
CREATE TABLE "table1_16581695_4" (
  "no_in_series" text,
  "no_in_season" text,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_airdate" text,
  "production_code" text
);
SELECT "production_code" FROM "table1_16581695_4" WHERE "no_in_season"='15';