2" groups at 15 yards is nothing to sneeze at! That's very good work even for veteran shooters. So, keep it up!
As far as your shots going left and slightly down, check the shots while shooting on a bag. This should help to see where your gun shoots relative to point of aim. Then, when you're still shooting left and low, you can compare how much. To me, it might be the trigger finger like you said. See about adjusting your grip so you can get a little more trigger finger on it and see how that works out for you.
Post pics of your targets and I'm sure much more experienced shooters will chime in.
Happy shooting and be safe!
Les Baer 1911: Premier II w/1.5" Guarantee, Blued, No FCS, Combat Rear, F/O Front, Checkered MSH & LBC Double Diamond Grips
Springfield Armory 4.5" XD-m 45 ACP
Springfield Armory XD-45 4" Service Model
M&P Shield 9 (wifes)
M&P 15 (Mine)