The last PrPro version that natively mated with the last SpeedGrade version is PrPro 2015.2.
You can download that in the Previous Versions section of the CC Desktop app's Program tab. Scroll down to PrPro, select Install, choose 2015 from the list, and after installation go ahead and "upgrade" that to the 2015.2 version. Also download/install SpeedGrade 2015.1.
Now ... on the SpeedGrade forum, a user has created an app that mods a project file from newer PrPro versions so that SpeedGrade 2015.1 can work the project file. Save your work and run back through the little app and the project file returns to format for the newest PrPro version again.
It actually changes only one character to do this.
There's a thread on that converter program near the top of the SpeedGrade forum. Patrick Zadrobilek's the creator ... and you'll see me there also. I use that darling little app myself.
Neil