Mix 4 tablespoons melted butter, 2 tablespoons sliced crystallized ginger and 3 tablespoons sugar in a large bowl; toss with 4 halved and pitted peaches. Place the fruit on a large sheet of foil; scatter 1 cup raspberries on top. Fold in the sides of the foil and seal to form a packet. Grill over medium-high heat until the peaches are tender and the berries are juicy, 15 to 20 minutes. Turn the peaches to coat in the berry sauce. Serve with vanilla ice cream or yogurt, if desired.