When was series premiere on the pilot episode
CREATE TABLE "table1_15823956_1" (
  "series" text,
  "episodes" real,
  "series_premiere" text,
  "series_finale" text,
  "region_1" text,
  "region_2" text,
  "region_4" text
);
SELECT "series_premiere" FROM "table1_15823956_1" WHERE "series"='Pilot';