Aside from the fact that you appear to care little for the disruption you will cause your fellow travellers, yes you can get off although if we were at the hold then too late chap.
However, why get on? You will know by the point you need to board how late the flight is running. An hour and a half is pushing it for a connection anyway so don't get on if it's running late.
You say you won't risk flying your first sector just in case you miss the next flight and therein lies your answer. Get an earlier flight or get a later connection.