CREATE TABLE table_27245 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( millions ) " TEXT)

Who wrote the episode that had 12.15 million viewers?
SELECT "Written by" FROM table_27245 WHERE "U.S. viewers (millions)" = '12.15'
SELECT "Written by" FROM "table_27245" WHERE "U.S. viewers (millions)" = '12.15'