A 12 vCPU, 24 GB RAM VM struggling with 100 synchronous quiz candidates? That doesn't sound right. I would expect the number to be four times that. There is something wrong.
Nobody can give you "ideas" other than speculations. You have to investigate your system. Performance will give you some orientation.
Nobody can give you "ideas" other than speculations. You have to investigate your system. Performance will give you some orientation.