If mitral valve regurgitation and prolapse already progressed from mild to moderate, how long usually it might take now to progress to severe?

In my experience this is quite variable. I've seen patients whose moderate mitral regurgitation never worsened through the years. Absence of left atrial enlargement,atrial dysrhythmias and hypertension are favorable factors. Your cardiologist will follow you closely and advise you.

This will depend on the cause and low long it took you to get to where you are. Best to discus with your Drs. Remember as Yoggi Berra said: "It is difficult to make predictions. Especially about the future".