Get your school money back. 50 mA * 300 = 15A.
Four strips of 15A makes 60A. You need a power supply of 60A.
According to the datasheet of the WS2815: Quiescent Current = 2.1 mA.
That means when all the leds are off, there is still a current of 2.1 mA * 300 * 4 = 2.52A.
That is 30 Watts energy wasted all the time.
I don't understand how much current a RGB led needs when it is fully on. According to the datasheet of the WS2815, the "RGB Channel Constant Current" is 15 mA. Is that for one color ? So the total would be 3 * 15 mA + quiescent current ?
Let's try again: ((3 * 15 mA) + 2.1 mA) * 300 * 4 = 56.52 A
That means you still need that power supply of 60A.
[EDIT] added "WS2815" in two places.