15.设m∈Rm\in Rm∈R,过定点AAA的动直线x+my+m=0x+my+m=0x+my+m=0和过定点BBB的动直线mx−y−m+2=0mx-y-m+2=0mx−y−m+2=0交于点P(x,y)P(x,y)P(x,y),则∣PA∣+∣PB∣\vert PA\vert +\vert PB\vert∣PA∣+∣PB∣的取值范围是((( )))