What's the most area of Bochum Part 2 with a population less than 15,911?
CREATE TABLE "main_places" (
  "place" text,
  "code" real,
  "area_km_2" real,
  "population" real,
  "most_spoken_language" text
);
SELECT MAX("area_km_2") FROM "main_places" WHERE "place"='bochum part 2' AND "population"<'15,911';