The 915 D3 head will have a flatter trajectory,lower launch and spin than a 915 D2 and there is a a spin difference between the 915 D2 and the 913 D2 as well.  What shaft is in the 915?  You can try putting your 913 shaft into the 915 head to see if it is the shaft that is making the most difference and you can also set it to a higher launch (D4 or A4).  If you were fit for this club, we would recommend talking with your fitter to see if he/she can take a look at your swing and what is happening.

Although the shafts say plus series, there is a not only a difference in the red, white and blue, but a difference between the 1st generation plus series and the second, newer generation.  As far as an exchange policy, you would have to inquire with your pro shop to find out what their policy is regarding trade ins.  We don't have any direct sales for shafts and don't sell or distribute heads.