How much is auto insurance for a 15 year old in Delaware?

There is no way to say what your premium costs would be simply by the age of the driver.

Insurance premiums are based on many factors including but not limited to;

The drivers age

The drivers length of driving experience

Any drivers training received

Prior losses or claims history

The type of vehicle being driven.

The area in which the driver operates the vehicle

The number of average miles driven

Vehicle usage

As you can see there are many factors that go into premium rating.