Usha,

I’ll find out what the reason is for this and if possible, provide you a Link for the release. 

I’ll get back to you as soon as I know more about it.

Thanks,

Janick

Usha, 

Is there a certain reason for the specific 8.15.15 Version?

The issue was addressed in 8.15.16, so we suggest installing Rockaway Iteration 14.
If you are running 8.15.15 in your Production org and need the same version in your sandbox again you can refresh the sandbox, that should do the trick. 

There has been an announcement about this issue here: https://community.skuid.com/t/challenges-with-installing-upgrading-skuid-on-salesforce-sp…

Janick