CREATE TABLE table_27058 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" FLOAT)

When 15 is the number in season what is the highest number in series?
SELECT MAX("No. in series") FROM table_27058 WHERE "No. in season" = '15'
SELECT MAX("No. in series") FROM "table_27058" WHERE "No. in season" = '15'