I have two reasons that I think D.D. won't get 1500 yards:
1. Tony Hollings - I think he replaces D.D about 10 plays a game. That will keep D.D. with fresh legs but it will take yardage away from him.
2. More emphasis on the passing game - the Texans ran a ton of draws and run plays on 3rd and 4th and long situations. They were forced to do so often because the defense was ravenged by injuries. I don't see us running nearly as often in those "long" situations this season.
Also, with an ever improving line, some offensive stability, and depth everywhere, I think we can let lose a bit more. I expect Hollings to get about 400-500 yards rushing and D.D. to only have around 1,200 when it is all over.