Filter high-frequency PWM but keep low-frequency modulation
Establish a low-pass=filter at 10% of the chopping frequency. Thus 20KHz.

A filter at 20KHz has TAU of 1/(2*PI*20KHx) or 50,000 microseconds/2*PI = 9 uSeconds.

You already have the R at 15 ohms. Simply place a 0.47uF cap from FET output to ground. Or any larger cap. This forms a parallel RC low pass filter.