It is adjusting the PIAs that you input for taking SS early or late. $15,000 ~ 75% of $20,136 so that sounds about right... I assume that you are ~62?
For him, $36,210 is about 132% of his PIA of $27,432 which reflects 4 years of delayed retirement credits at 8% a year, so I'm guessing that he was born between 1943 and 1954.
Now note what the present value would be for the recommended strategy. Then at the very bottom, test alternative claiming strategies of both taking now, both taking at age 65, both taking at FRA (full retirement age) and then you taking at FRA and him at age 70 and note the present value associated with each alternative.
I'm guessing that the present values of the various alternatives are not all that different.