CREATE TABLE table_24766 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( millions ) " TEXT)

What's the title of the episode first seen by 18.15 million people in the US?
SELECT "Title" FROM table_24766 WHERE "U.S. viewers (millions)" = '18.15'
SELECT "Title" FROM "table_24766" WHERE "U.S. viewers (millions)" = '18.15'