CREATE TABLE table_14148 ("Manufacturer" TEXT, "Transmission" TEXT, "Engine Capacity" FLOAT, "Fuel Type" TEXT, "L/100km Urban  ( Cold ) " FLOAT, "L/100km Extra-Urban" FLOAT, "L/100km Combined" FLOAT, "mpg-UK Urban  ( Cold ) " FLOAT, "mpg-UK Extra-Urban" FLOAT, "mpg-UK Combined" FLOAT, "mpg-US Urban" FLOAT, "mpg-US Extra-Urban" FLOAT, "mpg-US Combined" FLOAT, "CO 2 g/km" FLOAT, "Green Rating" TEXT)

What is the lowest combined mpg in the US for the A6 transmission, a CO2 g/km under 303, engine capacity over 2461, and L/100km urban (cold) of 15.9?
SELECT MIN("mpg-US Combined") FROM table_14148 WHERE "Transmission" = 'a6' AND "CO 2 g/km" < '303' AND "Engine Capacity" > '2461' AND "L/100km Urban (Cold)" = '15.9'
SELECT MIN("mpg-US Combined") FROM "table_14148" WHERE "CO 2 g/km" < '303' AND "Engine Capacity" > '2461' AND "L/100km Urban (Cold)" = '15.9' AND "Transmission" = 'a6'