CREATE TABLE table_38798 ("Driver" TEXT, "Constructor" TEXT, "Laps" TEXT, "Time/Retired" TEXT, "Grid" TEXT)

Who was the constructor of the car that went 56 laps and had a grid of 15?
SELECT "Constructor" FROM table_38798 WHERE "Laps" = '56' AND "Grid" = '15'
SELECT "Constructor" FROM "table_38798" WHERE "Grid" = '15' AND "Laps" = '56'