"Collins knows what every NFL D does, that's obvious."
I would disagree. According to pro football focus, Siemian's problems start when you put pressure on him. If you can't read coverage's , see a safety or you lock onto one receiver from the snap, there is no way you can complete 70% of your passes whether the pocket is clean or not. Want to beat the Broncos? Get to Siemian. Blitz him...pressure him...hit him. He'll start looking for his first read the minute he loses confidence in the lines ability to protect him. 
The Little Guy