Could Not Find Developer Disk Image - Xcode 7.2 & IOS 9.2

I have just updated my iPhone 6S to iOS 9.2, and for a while I couldn't run Xcode apps on it because I didn't have Xcode 7.2 and I would get the "Could not find Developer Disk Image" error. I have now updated to Xcode 7.2 and still get the error.

I am running OS X Yosemite–can't install El Capitan because of an error ("This Core Storage operation is not allowed on a sparse logical volume group").

Any idea on how to proceed?

When I installed El Capitan (got rid of the "This Core Storage operation is not allowed on a sparse logical volume group" error by activating FileVault on my Mac), I saw an Xcode dialog box saying it needed to install additional components.

I am unsure whether that dialog box was there before I upgraded OS X or not, as it might have got lost amidst other application windows. Either way, that seems to have installed the disk image needed to run apps on the iPhone.

EDIT: This indeed did not solve the problem. I realized my Mac was still running Xcode 7.1.1 instead of 7.2, even though the Mac App Store said it had updated to 7.2. What I did is delete both Xcodes from the /Applications folder and reinstall 7.2 through the Mac App Store.