Presumably 15% of the registered voters rather than share of the vote. I suspect the same is true for the Dowd statistic. If it were otherwise it wouldn't be such a safe seat.

In any case this is irrelevant to the subject matter. Hope the kids are ok and that the perpetrators are dealt with appropriately. The school is good and the children that attend are generally well-behaved. When I was their age, 20 long years ago, there used to be groups who would go off and fight rival schools. Picking on younger kids is worse than that. Pathetic cowardice as well as bullying.