To create an equation relating the cost \( C \) to the number of people \( P \), we can express the cost as:
\[ C = 30P \]
where \( C \) is the total cost in dollars and \( P \) is the number of people.
Now, to find the cost of admission for 15 people, we can substitute \( P = 15 \) into the equation:
\[ C = 30 \times 15 \]
Calculating this gives:
\[ C = 450 \]
Therefore, the cost of admission for 15 people is \( 450 \) dollars.