Prepare the Simple Syrup: In a medium saucepan, combine 1.5 cups of sugar with 1.5 cups of water. Heat over medium heat, stirring gently until the sugar dissolves completely, about 5 minutes. Remove from heat and cool.

Squeeze the Lemons: Juice enough lemons to yield 2.5 cups of fresh lemon juice. Strain through a fine-mesh sieve.

Combine Ingredients in a Pitcher: Pour lemon juice into a large pitcher and add 6 cups of cold water. Stir well to combine.

Sweeten to Taste: Gradually pour the cooled simple syrup into the pitcher, stirring continuously to achieve desired sweetness.

Chill and Serve: Refrigerate for at least an hour. Serve over ice, garnished with lemon slices or mint.