What is the perimeter for a 15 square units?

Answer 1

There is not enough information.

First you need to know what shape: circle, ellipse, triangle, square, other quadrilateral, a polygon with 5 or more sides.

Then you need some information on whether or not the shape is regular. If not, you need more information on the relationships between the sides.

The more informative your question is, the more informative the answer will be.