CREATE TABLE table_16537 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original air date" CLOB, "U.S. viewers  ( millions ) " CLOB)

How many millions of viewers watched episode 15?
SELECT "U.S. viewers (millions)" FROM table_16537 WHERE "No. in season" = '15'
SELECT "U.S. viewers (millions)" FROM "table_16537" WHERE "No. in season" = '15'