CREATE TABLE table_53633 ("Manufacturer" TEXT, "Type" TEXT, "Quantity" FLOAT, "PTRD Nos." TEXT, "GWR Nos." TEXT)

What is the highest Quantity for PTRD Nos. 3, 15?
SELECT MAX("Quantity") FROM table_53633 WHERE "PTRD Nos." = '3, 15'
SELECT MAX("Quantity") FROM "table_53633" WHERE "PTRD Nos." = '3, 15'