How often is he changing the filter?
If he is one of the "change filter every second oil change" guys then i think "lunatice" does not do him justice
If he is changing the filter every time then it starts to eat into any cost argument. eg
2 x Dino + 2 x Filter is likely to be closer in total cost to 1 x Synth + 1 x Filter.
While the above detail adds to the background, it does not change my recommendation. Of the two choices I vote for "Synth every 3000".
I think Dino every 1500 is manifestly insane under all but the most strange conditions (eg something like driven all city miles in extreme temperatures a total of only 1000 miles a year). As others have posted, there has recently been some interesting data showing that oil often shows lowest wear numbers somewhere around 2000-3000 miles in. So your friend doing Dino changes at 1500 may actually be doing more harm than leaving it in for 3000.
On the other hand I change my GF's oil about every 2000 miles, because it takes her 6 months to do that and her trips are mainly two or three miles. I just figure that with short trips like that a twice year OCI is worth it.
I admit to doing many 3000 mile changes of Mobil 1 and Mahle filters in my Porsches. Do I think it was necessary? No. Wasteful? Possibly. But generally these were motivated by things like changing grade for seasonal reason, having the car in for service for other reasons. My current Pcar will not be Winter driven so I no longer worry about seasonal grade changes. For the 7 months a year it is driven a total of about 5500 miles it will get a fill on 0w40 synthetic. Once a year OCI now.