Hi Anders, With the same grip at the same length, the swingweight should be D3 in both drivers with that shaft.  That being said, go to your fitter and try another weight to see if that helps you with your timing or you can also put a lighter grip on it to see if that helps.  Or you can also have your pro shop set up a Warranty check and we will bring it in and check the swingweight for you.

Thanks - I am seeing the guys at St Ives on the 6th May to get this rectified. 

First I had a like for like: 915 YS6 S Shaft D3 and could not get the ball airborne. Moved to the D2 in the hope of better launch and its better but still very inconsistent and the ball flight still is not what I am used too. I play of plus 2 so I know what I am looking for ball flight etc. Both the 915 D2/3 have a very flat ball flight and the distance is way off. I compared it to my old driver last night and the difference was huge

Im not really sure but i suggest you go to your nearest pro shop to see whats the problem.