The error message is
The iOS 8.2 simulator runtime is not available.
Unable to open liblaunch_sim.dylib. Try reinstalling Xcode or the simulator runtime.
I've checked XCode preferencaes -> download tab and it seems that extra simulators can not be installed.
In Apple's release notes for Xcode 7 beta found here: http://adcdownload.apple.com/WWDC_2015/Xcode_7_beta/Xcode_7_beta_Release_Notes.pdf
"Xcode 7.0 beta does not support iOS 8.4 and earlier simulator runtimes. (20699475)"
My experience has been that beta versions of XCode only support a single iOS version.
You would need to use a release version of XCode to do that.
In Apple's release notes for Xcode 7 beta found here: http://adcdownload.apple.com/WWDC_2015/Xcode_7_beta/Xcode_7_beta_Release_Notes.pdf
"Xcode 7.0 beta does not support iOS 8.4 and earlier simulator runtimes. (20699475)"
" Xcode 7.0 beta now supports downloadable legacy simulators. (20699475)"
This is found in the Xcode 7 beta 3 release notes found here
Still bugged in the GM release...
Have a look at this SO answer, it might provide a (hopefully temporary) fix
The updated iOS 8.x simulators should work fine with Xcode 7.0. Make sure you've downloaded the relevant updates from Xcode's preferneces.
iOS 7.1, however, does not.
Still having this problem with the Xcode 7.0.1 when trying to install the iOS 8.4 simulator.
Then this isn't the thread you're looking for. Please search for a relevant thread for your specific issue or start a new one if you can't find it.