1. **State the problem:** We are given a rectangle with length $x^2 + 8x + 15$ and width $x + 3$. We need to find the length in meters, which is the expression for the length side. 2. **Recall the formula for the area of a rectangle:** $$\text{Area} = \text{Length} \times \text{Width}$$ 3. **Factor the length expression:** $$x^2 + 8x + 15 = (x + 3)(x + 5)$$ 4. **Interpretation:** Since the width is $x + 3$, the length $x^2 + 8x + 15$ can be factored as $(x + 3)(x + 5)$, which means the length is $x + 5$ times the width $x + 3$. 5. **Conclusion:** The length of the rectangle is: $$\boxed{x + 5}$$ meters. This shows the length side is $x + 5$ meters, given the width $x + 3$ meters and the original length expression $x^2 + 8x + 15$ meters.