Fifteen mages. Five with explosive devices, and ten without. Though all those with explosive devices in their mouth that I have encountered weren't expert level mage, I shouldn't think that's the case now. After all, we have defeated a lot of them and captured them. Though I don't know if the cult knows that we captured them or not. There were no witnesses after all.
But the cult should be suspicious how there are too many expert level mages who never returned from their mission. As for the artificial master level mage who died, the Professor seems to never told about their deaths to the cult as he wanted to monopolize the Black Slime alone. Or at least that's what Albert know after interrogating him.
Just because all fifteen of them are expert level mages, doesn't mean I can't defeat them. None of them realize that I was so close to them listening in.