I wouldn't say 'often' implies >50%, to imply that I would use something like 'mostly' or 'generally'. I think if you think about a 15% failure rate in something else, for example starting a car, saying it often fails would be pretty apt.

Context matters, 15% failure rate for a weaopon is certainly often. Furthermore, what that means in the context of cluster munitions is that they just sit there long after the conflict is over, so when people stumble on them decades later they get maimed and killed.

This is currently happening in places like Vietnam that were subjected to these horrors by US. Now it's going to be the turn for the people of Ukraine.

Any pretenses that US actually cares about the people of that country have now been dropped.

One in six fails to detonate in a cluster munition that has around a hundred grenades? Holy fuck that's fifteen unexploded grenades on a former battlefield every time they fire the weapon, I was previously against cluster munitions and I was just assuming it was like a 1% failure rate.