To find the total weight of all the vegetables in Lars's baskets, we multiply the weight of vegetables in each basket by the number of baskets.
Each basket contains \( 1 \frac{1}{2} \) lb of vegetables. We can convert this mixed number to an improper fraction:
\[ 1 \frac{1}{2} = \frac{3}{2} \text{ lb} \]
Now, Lars has 10 baskets, so we multiply the weight in one basket by the number of baskets:
\[ 10 \times \frac{3}{2} = \frac{30}{2} = 15 \text{ lb} \]
Since 15 is a whole number, we can express it as a mixed number:
\[ 15 = 15 \frac{0}{1} \]
Thus, the total weight of all the vegetables in the baskets is
\[ \boxed{15} \]