In addition to the cmd+1, cmd+2 and cmd+3 options under Window->Scale that zoom to 100%, 75% and 50% respectively, you can also kind of do a custom zoom amount by setting a custom preference. Namely, try setting the SimulatorWindowLastScale preference in the com.apple.iphonesimulator.plist file under ~/Library/Preferences directory. Running the following command in a terminal worked for me to be able to see the full screen of an iPad Air with iOS Simulator 8.2:
defaults write ~/Library/Preferences/com.apple.iphonesimulator SimulatorWindowLastScale "0.4"
See also https://apple.stackexchange.com/a/93313