I haven't seen a good replay on the first one they called in OT, but the placement of the ball after the foul indicates it came earlier in the route than all of the replays showed. And the asinine roughing the passer that happened on the same play made it effectively a two-yard penalty on top of that 15.
But the second one, he did gain separation. He was like two yards from the defender on the route. He slowed down a little to attempt the catch and that's when the DB gained ground and swiped, making early contact with the arms of the receiver. It would be a good call in the 1st quarter, and ideally they shouldn't have different standards for OT.
If anything needs to be changed, it's the yardage. Make it a 15-yard penalty. Maybe add discretion to make it a spot foul for an intentional foul that clearly prevents a score. There's nothing inordinate about DPI that needs to make it a spot foul and effectively award points. Assuming the catch would be made is a stretch on a lot of these. They can be fouls without being 30-yard fouls. Especially when on the other hand an OPI is a mere 10-yard penalty.
Bills have no one to blame but themselves.