Generally, as rule of thumb, before pulling the the cheating card you wanna look at all the variables first. How good are the alleged cheaters? How good are the opponents? How well do you yourself understand the game?
3v15 is tough but not impossible given the right circumstance. I’d have to see a video to see exactly what’s going on, I don’t really take anecdotal claims seriously. If you’re in doubt, report em and let zos be the judge.