If you are not on a More Everything plan, when you try to activate the HotSpot, you will get a message instructing you to call Verizon, or that the service is unavailable. However, you can log into My Verizon on a PC or the My Verizon app on your phone and you can see the name of your plan right there .
You mention a 15 GB data plan. when you use the hot spot on ypur phone, it will show "tethered data" in ypur settings under data use. There is no extra charge for using your existing data pool in this way.