On a math note, if I understand you, the "given" vectors are the row vectors of the matrix {{-3,2},{-15,8}}, that is the vectors {-3, 2} and {-15, 8}. I do not think there is any general relationship between the row vectors and eigenvectors of a matrix.
The first column of a matrix mat is the vector you get from the product mat.{1,0}. The second column is the result of mat.{0,1}. An eigenvector is a (nonzero) linear combination of the columns that happens, when multiplied by mat, to yield a scalar multiple of itself. (Of course, every product mat.{x,y} is a linear combination of the columns of mat, so the scalar-multiple property is key for eigenvectors.)