If you make stop the premium payments after three years then the policy acquires a Paid Up Value for a Reduced Sum Assured. You Sum assured will also reduce in proportion to premiums Paid by you. As you said if you stop the policy in 3rd year, (assuming your Sum Insured is 10 lacs), your sum assured will reduce from 10 lacs to 2 lacs (20%), as you have paid the premium only for 20% of the tenure (15 years).