The output voltage of an op amp is limited by its supply voltages. So best case (rare and expensive but possible with ideal op amps), the output voltage could range between +15 V and -15 V if those are the supply voltages. In real op amps the output can usually only approach the power "rails" as they're called, so maybe +13 to -13V for this example.
An op amp has two power supply pins, one positive and one negative. The notation +/-15 V indicates the positive supply is 15V and the negative supply is -15V.
Note there is no (power) ground pin on an op amp (although one or more pins may be grounded, depending on the circuit configuration), which certainly struck me as odd when I first encountered it :)
Also note there is such thing as a so-called "single supply" op amp, which is designed to be useful when the positive supply is, say +12V and the negative supply is 0V (ground).
If op amp 1 in your circuit can put out between +/- 15V and op amp 2 in your circuit can put out between +/- 15V, I think you have the basic ideas you need to reason through your question :)