My friend plays FIFA 15 on Android while I have the game on PS4. Am I able to play FIFA online with him?
FIFA 2015 for PS4 and FIFA 15 Ultimate Team for iOS/Android are technically different games and do not support online play with each other. The same goes for FIFA 2016 and FIFA 16 Ultimate Team.
Playing FIFA 15 across different types of devices is not supported. Each platform has an individual online gaming system. You can neither play PC to PS4 or XBox (link for FIFA 16), or those two with each other.
I cannot find any official resources to back this up, but it stands to reason that playing from phone, which has fundamentally different controls, to one of the full fledged platforms will not work either.
However, you can use the Android software Remote Play as shown in this video to use your Android device to remote control a PS4 and play like that.