lack of freeing bounding boxes is only a sign of poor implementation. nothing else. it's no excuse.
"was person in box checks" can be done pretty fast. origin to origin can also be done properly if your extending it to spheres, because there are plenty of early out tests that can be done on sphere-sphere collision, including testing if the spheres WOULD HAVE collided with each other even though it may not be evident from the original and next frame.