Oksana and her three friends are heading to a concert. They paid $540 in total for tickets. This included insurance for $15 for each person. How much was the cost of one ticket to the concert?

To find the cost of one ticket to the concert, we first need to determine how much money was spent on the tickets alone, excluding the insurance.

1. **Calculate the total insurance cost:**
Since there are four people (Oksana and her three friends), and each person paid $15 for insurance, the total insurance cost is:
\[
\text{Total Insurance} = 4 \times 15 = 60 \text{ dollars}
\]

2. **Determine the total amount spent on tickets:**
Now, we can find out how much was spent on tickets by subtracting the total insurance cost from the total amount paid:
\[
\text{Total for Tickets} = \text{Total Amount Paid} - \text{Total Insurance} = 540 - 60 = 480 \text{ dollars}
\]

3. **Calculate the cost of one ticket:**
Since there are four people, we divide the total amount spent on tickets by the number of people:
\[
\text{Cost per Ticket} = \frac{\text{Total for Tickets}}{4} = \frac{480}{4} = 120 \text{ dollars}
\]

Thus, the cost of one ticket to the concert was **$120**.