Given diameter d = 1.5 mm = 1.5 x 10⁻³ m.

Given diameter $d = 1.5 \text{ mm} = 1.5 \times 10^{-3} \text{ m}$.
The radius $r$ is half of the diameter:

$$r = \frac{d}{2} = \frac{1.5 \times 10^{-3} \text{ m}}{2} = 0.75 \times 10^{-3} \text{ m}$$

The cross-sectional area of a circular wire is given by $A = \pi r^2$.

$$A = 3.14 \times (0.75 \times 10^{-3} \text{ m})^2$$ $$A = 3.14 \times (0.5625 \times 10^{-6} \text{ m}^2)$$ $$A = 1.76625 \times 10^{-6} \text{ m}^2$$

Given resistivity $\rho = 1.7 \times 10^{-8} \Omega \text{ m}$ and length $L = 20 \text{ m}$.

$$R = (1.7 \times 10^{-8} \Omega \text{ m}) \times \frac{20 \text{ m}}{1.76625 \times 10^{-6} \text{ m}^2}$$ $$R = \frac{34 \times 10^{-8}}{1.76625 \times 10^{-6}} \Omega$$ $$R = \frac{34}{1.76625} \times 10^{-2} \Omega$$ $$R \approx 19.249 \times 10^{-2} \Omega$$ $$R \approx 0.192 \Omega$$

The resistance of the wire is $\boxed{\text{0.192 } \Omega}$.