Drum exercise BPM do not add up
Trombonist here.
Assuming each bar is in $\frac{4}{4}$ time, we have $16 \cdot 4 = 64$ quarter note beats per phrase. Each phrase is repeated $20$ times, for a total of $64 \times 20 = 1280$ quarter notes. Now your metronome is set to $152$ BPM (i.e., quarter-note 152), so doing this exercise completely should take $\frac{1280}{152} \approx 8.42$ minutes.
Your mistake is treating each sixteenth note as a beat - unless, of course, your time signature is $\frac{k}{16}$. That requires a difference calculation.