Depending on the university you attend, usually if you fail a class, you retake it. But failing one test worth 15% won't mean much. However, if you fail another exam then usually they take you in for assessment and see what went wrong and whether you should continue your studies with a retake OR expulsion from the course all together. This is what I was told though from a cousin who is a professor at university. But I am pretty sure this system only exists in the elite unis like usyd, unsw, unimelb, etc. But every other uni I think it is if you fail 3 exams. You should talk to your professor/lecturer and see what went wrong and seem like you actually care about you failing the test. Just keep trying for the future exams.