The given scenario above is like a geometric sequence with r or common ratio being 1.05 and the first term being 31 square meters. The nth term of the sequence is calculated through the equation,
A15 = (A1)(r)^(n - 1)
Substituting,
A15 = (31)(1.05)^(15 - 1) = 61.3778 square meter
Therefore, the area covered by the spill after the 15th day is approximately 61.4 square meters.