"Percakapan ini memperlambat selesainya pekerjaan saya."
Translation:This conversation slows down the completion of my work.
Another alternative which is correct, "This conversation slows down completion of my work." The word "the" is not required here. And another alternative, "This conversation slows the completion of my work.", should also be accepted. "Slows" and "slows down" are equivalent, "down" is not required.