I believe you are asking about IRS Form 8615 - there is no Form 8515. Here are the IRS rules as to when Form 8615 must be filed:
Form 8615 must be filed for any child who meets all of the following conditions:
1. The child had more than $2,100 of unearned income.
2. The child is required to file a tax return.
3. The child either:
a. Was under age 18 at the end of 2016,
b. Was age 18 at the end of 2016 and did not have earned income that was more than half of the child's
support, or
c. Was a full-time student at least age 19 and under age 24 at the end of 2016 and did not have earned
income that was more than half of the child's support. (Earned income is defined later. Support is defined
below.)
4. At least one of the child's parents was alive at the end of 2016.
5. The child does not file a joint return for 2016.
For these rules, the term “child” includes a legally adopted child and a stepchild.
These rules apply whether
or not the child is a dependent.
These rules do not apply if neither of the child’s parents were living at the end of the year.
https://www.irs.gov/pub/irs-pdf/i8615.pdf
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
