CREATE TABLE table_56595 ("Driver" TEXT, "Constructor" TEXT, "Laps" FLOAT, "Time/Retired" TEXT, "Grid" FLOAT)

what's the average grid that has a time/retired piston and laps smaller than 15?
SELECT AVG("Grid") FROM table_56595 WHERE "Time/Retired" = 'piston' AND "Laps" < '15'
SELECT AVG("Grid") FROM "table_56595" WHERE "Laps" < '15' AND "Time/Retired" = 'piston'