USB to male bullet connector
USB ports are not designed to provide that much power.

\$P = V \cdot I \quad \Rightarrow \quad I=\frac PV\$

To calculate your desired output power:

\$P = 15V \cdot 1.5A = 22.5W\$

Now, to relate this to the input:

\$I = \frac PV = \frac {22.5W}{5V} = 4.5A\$

So, you would need to draw 4.5 A from the USB port.

USB 2.0 limits the port output to 500mA (0.5A). There are other USB options: A high-capacity charger might provide you 2.2A.  There's a newer "power delivery" spec which allows for 3A.  Unfortunately, all of these are insufficient for your application.