My advice would be to just get the same shaft if you liked it. Confidence is a large part of the game and if you liked it than use it. The other thing you good do is take your old driver and find out the swing weight and all the tech stuff and have a PGA Professional tell you what matches up.

Dianama 60 or 70 depending on what you want unless you have a Titleist fitting centre anywhere near.

Best thing to do would be to talk with a local Titleist fitter about what would be comparable to the Aldila NVS shaft you currently use.
However, since you already have your 915 with a shaft, you could simply buy another Aldila NVS shaft and have your club repair person/shop remove the SureFit adapter from the current shaft and install it on the NVS shaft.

I would start by talking with the fitter.