It’s not about “chores” it’s about taking responsibility for yourself and for the home you live in.
At 15 yo he should be able to do laundry, iron, cook basics, know how to clean floors, kitchen and bathrooms.
That’s not to say he should be expected to do those things all the time but that he should have been taught how and understand the importance of those activities to keeping your home healthy and happy.
I had a friend who was genuinely shocked to discover how much effort it took to shop, plan meals and cook, clean the house and do laundry every day.
He had this epiphany shortly after his divorce. 
Our rule is that if you are asked to help with something you pitch in without complaint.
So the D.C. don’t load the dishwasher, put out the bins, Hoover, dust etc every day but at 11yo they know how and help if asked. They are certainly expected to clean up after themselves.
They can both iron basics and are learning to cook.
I’m determined to ensure that they start adulthood fit to be considerate flat mates or partners.
Do you really want a future DIL to be questioning you and his father why you so ill prepared your DS for the basics adult life?