CREATE TABLE table_28550 ("Series #" FLOAT, "Title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original air date" CLOB, "Production code" CLOB)

Name the original air date for series number 15
SELECT "Original air date" FROM table_28550 WHERE "Series #" = '15'
SELECT "Original air date" FROM "table_28550" WHERE "Series #" = '15'