In a large pot bring 4 1/2 cups of water to a boil over high heat. Stir in the rosehips and raisins. Partially cover the pot, lower the heat, and simmer for 10 minutes. Remove pot from heat, stir in raspberry leaves, cover, and steep for 10 minutes.
Meanwhile, place a large strainer lined with cheesecloth or a damp paper towel over another pot or heatproof bowl. Strain tea, pressing on the herbs to extract all liquid. Add raspberry and orange juices and stir to blend. Let brew cool completely, about 45 minutes. Fill four tall glasses with ice. Pour tea over ice and garnish each with an orange slice, if desired. Serve immediately.