I wouldn't cycle over 15% body fat. And if you're on TRT you would just go back to your normal levels when you're done. It's not to stop sterility pct is to regenerate your body's natural production of test which you don't need to worry about.
If you're losing weight stick to a good diet and training then hit the gear when you're in better shape. You have to be trained and in good shape when you start so you avoid injuries