If a person were to miscarry a month & a half after conception, would there still be heavy bleeding and cramping? and how long would it take to bleed?

Impossible to tell: The pregnancy can stop growing at any point after conception, but the actual bleeding and expelling can take much longer to start happening. So the amount of tissue you need to pass can be quite variable depending upon how big the pregnancy grew before it stopped. Unfortunately, that process is different for everyone, and for some it doesn't end, and they need a d;c to complete it.