To calculate the experimental probability that the next appliance Leah sells will be an oven, we first need to find the total number of appliances she has sold.
The number of each appliance sold is as follows:
- Washing machines: 3
- Dishwashers: 1
- Ovens: 6
- Clothes dryers: 5
Now, we calculate the total number of appliances sold:
\[ 3 + 1 + 6 + 5 = 15 \]
Next, we find the number of ovens sold, which is 6.
The experimental probability \( P(\text{oven}) \) is calculated as the number of ovens sold divided by the total number of appliances sold:
\[ P(\text{oven}) = \frac{\text{Number of ovens sold}}{\text{Total number of appliances sold}} = \frac{6}{15} \]
We can simplify this fraction:
\[ \frac{6}{15} = \frac{2}{5} \]
Thus, the experimental probability that the next appliance Leah sells will be an oven is:
\[ \boxed{\frac{2}{5}} \]