In general, when loft is increased, spin will also increase

Eric, if you are trying to keep spin down, it may be a good time to step up the 915's in a few months...they may have lower spin overall...I have felt a difference when I went from the 910 to 913's... IMHO

The neat thing about the adjustments is you can try them and return them if they don't improve what you had.  The adjustment to 11.25 will change setup from 0.5 open to 0.5 degrees closed, and to 12 degrees will close the face a little more.  It won't cure a slice, but can reduce fade.  If that doesn't solve your issue, shafts can also affect flight path, and that may be a solution.  Getting fitted with a new shaft for a 910 is hardly worth it, since you lose the option of getting the loft optimized and the 10.5 may not be the best solution.  The final cost + a trade-in of the 910 is not that much less than a new 915.  The low cost option is buying a used club for the shaft, but then you would only be guessing on the best combination for you.