int wincount=0, totalcount=0;
for (int i=1; i<=6; i++) {
    for (int j=1; j<=6; j++) {
        for (int k=1; k<=6; k++) {
            … // insert more loops here
            if (i+j+k+… >= 15) {
                wincount++;
            }
            totalcount++;
        }
    }
}
float probability = wincount/totalcount