FYI
All simulators are packed with Xcode app. Instead of installing simulators you can just install the specific Xcode versions.
Xcode7.0 has iOS9 Simulators
Xcode6.4 has iOS8.x Simulators
In your CI testing if you want to test you app for a specific simulator just select xcode version before you do the xcodebuild command
xcode-select -switch <path to your xcode app>
This will set your default xcode to run the xcodebuild
Then run the xcodebuild with your respective simulator.
xcodebuild -configuration ${BUILD_TYPE} -target ${TARGET_NAME} -arch ${CPU_ARCHITECTURE} -sdk ${SIMULATOR_OR_IOS_SDK}
In the place of SIMULATOR_OR_IOS_SDK
give your simulator value.
You can find the simulator value by running
xcodebuild -showsdks
This will show like
OS X SDKs:
OS X 10.11 -sdk macosx10.11
iOS SDKs:
iOS 9.1 -sdk iphoneos9.1
iOS Simulator SDKs:
Simulator - iOS 9.1 -sdk iphonesimulator9.1
tvOS SDKs:
tvOS 9.0 -sdk appletvos9.0
tvOS Simulator SDKs:
Simulator - tvOS 9.0 -sdk appletvsimulator9.0
watchOS SDKs:
watchOS 2.0 -sdk watchos2.0
watchOS Simulator SDKs:
Simulator - watchOS 2.0 -sdk watchsimulator2.0
This way you can build your project on any specific device/simulator/os.
Hope this helps :)