Let's look a little deeper.
Litton first 4 games:
Norfolk - 24-31-270 4-0
Very good game against a very bad FCS team at home. Win.
Kent State - 14-36-151 2-2
Very bad game against a bad FBS team on the road. Completed about 40% of his passes. We won in double overtime, only got to overtime due to a Reeves KOR for TD.
ODU - 21-35-212 2-0
A win against a fairly poor ODU team at home. Solid game, but not spectacular.
USM - 11-21-163 2-1
Another win against a pretty good USM team that year. Defense held USM to 10, Litton was unimpressive in this game and not asked to do much, with only 11 completions.
Four game totals - 70-123-796 10-3 57% completion. 4-0 record
Green first 4:
Miami - 24-37-272 2-0
Good debut against a bad FBS on the road. Win
EKU - 23-39-278 3-1
Solid performance against a decent FCS at home. Win
NCST - 22-43-270 1-2
Tough outing against a P5 with the #9 scoring defense nationally. Loss
WKU - 18-39-288 2-3
Rough outing on the road, big 98 yard drive to get the lead in the 4th on last possession. Win.
Four game totals - 87-138-1,108 8-6 55% completion. 3-1 record
The two biggest differences are that Green has thrown more picks, even though 3 of the 6 weren't on him they still count, and Green has played a tougher schedule. Norfolk, Kent and ODU were all really bad in 2015. EKU, Miami and WKU are bad, but better as a group than those teams were. NCST is better than USM was in 2015.
We are also more vertical in the passing game. Chase was given a pretty steady diet of short, safe throws where Green is going intermediate and long more. That's why, even though he has a slightly lower completion percentage, he is averaging over 7 yards per attempt while Chase averaged 6.4 through 4 games in 2015.
The bottom line to this is that Green is playing every bit as well as Chase did starting out. Give him some time.