Shloka 15.7 said the soul attracts the mind and senses. Shloka 15.8 said these travel with the soul. Now 15.9 tells us what the soul does with them: it experiences the world. Through the ear it hears, through the eye it sees, through the skin it feels, through the tongue it tastes, through the nose it smells. And behind all five stands the mind, directing attention.
The mind is the sixth sense here — not in any supernatural way, but as the coordinator. It decides which sense object to pursue and which to ignore. The soul, seated within, uses all six as its instruments of engagement with the world.
None of this is described as wrong or sinful. Krishna is simply stating how things work. A house has windows — light comes through, and so does dust. The senses are those windows. They connect the inner being to the outer world.