2.7 COP is a a noticeable improvement but still terrible at those temperatures. Are you sure it’s 6.6 kW?

PS: 2.7 COP * 0.665 = 180% efficiency which still crushes the 80% heat pump in your example but these numbers should be much higher.

15 SEER is garbage American manufacturers dump on people. Asian manufacturers are making 25-35 SEER systems.

15 SEER relates to cooling efficiency, what is its HSPF rating?