One method is to use two current mirrors facing each other across the output connection. One from the + supply and one from the - supply. These mirrors are driven from variable current sources referenced to ground. This makes their input voltage range within the +-15V output capability of op amps. Then sense the output voltage through a resistor (that is rated at 7 kV) and use an inverting op amp circuit with the inputs diode clamped to the +-15V supply to protect the op amp.