This 78015 IC is a 15V Voltage Regulator that restricts the output voltage to 15V output for various range of input voltages. So as the name suggests, the voltage regulator is a circuit that is used to regulate (fix) the voltage fluctuations in the input and therefore, makes the circuitry safer. LM7815 is an extremely popular and easy to use linear voltage regulator for generating a regulated 15V. It is a easy and simple to use voltage regulator with no external circuitry or components needed for voltage regulation (except for a few smoothing capacitors). It can provide around 500 mA of current without an heatsink and upto 2 A with an heat sink.
Note:This regulator has a ~2V linear drop-out. That means you must give it at least 18V to get a clean 15V out.