Final answer:
The total number of outcomes is 15.
Step-by-step explanation:
To find the total number of outcomes, we need to multiply the number of sizes of milkshakes by the number of flavors of ice cream. In this case, there are 3 sizes of milkshakes (S, M, L) and 5 flavors of ice cream (Vanilla, Chocolate, Strawberry, Mint, Lemon).