My daughter is 18 and she has never liked the woods, lake, cabins, camping. She did however have 2 good experiences at summer camp at the ages of 9 and 10. By middle to high school she was too old for that (in her mind) and like your son, she loves the busy city.
If he is 15 he can have a part time job.
I have a 15 yr old neighbor boy who helps us when we get a load of dirt delivered. I give him a minimum of $40 and then $10/hour. He loves it. It is hard work but it does not take long to finish 6 yrds of dirt when 2 people are working at it.
I know the local grocer here has baggers that walk everyone to the car so no carts are left in the parking lot. They hire a lot of local teens to do this and many of the teens end up with more responsibility and bigger jobs as they prove themselves. It is a great avenue to start working around 14-15.
The movie theatres also hire younger teens for selling concessions and taking ticket stubs. Maybe that would interest him along with the free movies!!
My daughter is on my payroll for our company and learning how to run a business, very minimal hours but she is starting college in the fall and she in entering business so this is a way for her to gain some experience. She does babysit a lot for a few families in our neighborhood and makes good money with that job.
I completely agree that they need to be active and busy but I don't want to take all the summer fun away either. It is a balance. Right now, my daughter is anxiously getting all of her dorm décor together, painting, reading and running. Right now she is cooped up on day 4 from wisdom teeth removal, yuck and is still in soft foods and movies.
Good luck!!