If it's a RCD, there may be a current leak to the ground, or the 'apparent' power may be over 15A. It may mean that your saw power factor [a.k.a. cos(fi)] is lower than 0,82 (check on the label).
15 < P*cos(fi)+P*sin(fi) where fi is between 0 and 90 (in your case cos(fi) is lower than 0,82). In your case P*sin(fi)=10 so we can go to fi < 63°.
