We have the two equations:
1) \( 2x + 3y + 15 = 0 \)
2) \( 3x - 2y - 12 = 0 \)
To determine the relationship between these lines, we compare the slopes of the two lines. The slope of a line \( ax + by + c = 0 \) is given by \( \text{slope} = -\frac{a}{b} \).
For the first line, \( 2x + 3y + 15 = 0 \), the slope is:
\[
\text{slope}_1 = -\frac{2}{3}.
\]
For the second line, \( 3x - 2y - 12 = 0 \), the slope is:
\[
\text{slope}_2 = -\frac{3}{-2} = \frac{3}{2}.
\]
Since the slopes are not equal, the lines are not parallel. Therefore, they are intersecting straight lines.
Thus, the correct answer is \( \boxed{\text{Intersecting straight lines}} \).