CREATE TABLE table_1781 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( million ) " TEXT)

Who wrote the last episode (episode 15) of season 3?
SELECT "Written by" FROM table_1781 WHERE "No. in season" = '15'
SELECT "Written by" FROM "table_1781" WHERE "No. in season" = '15'