You can add your face to your custom Superstar in WWE 2K15, but only in the Xbox One and PlayStation 4 versions of the game.
If you have one of those consoles and would like to add that extra bit of customization to your custom character, then you should head over to the WWE blog and check out the video tutorial that will walk you through the process.
NOTE: You will need access to image-editing software (such as Photoshop) in order to do customize your Superstar in this fashion.