He sounds all very normal.
It is tiring, but I think it's great that he's willing to explore on his own for 15mins. Keep doing what you're doing. He is actually being independent by being off by himself for that amount of time. The way for him to actually grow independently is to know that you ARE there for him as he needs it and then he'll continue to go off and do his thing because he's safe in knowing you're there as needed. Has he got the whole house to explore? Maybe set up a little discovery trail or something for him to amuse himself with while crawling, cushions to crawl over, tunnels to go through, crunchy paper to screw up, pots and pans to bang things in. It takes a bit of creativity I know. Have him explore the different rooms you're in while doing chores or whatever you need to be doing and involve him as much as possible. In the kitchen I set up a drawer with my ds's cups/bowls etc and some toys that he could access and play with when I was in there.
My ds was way over the jumper by the time he was crawling at 7mths, I packed it away, life was for exploring not being contained - my dd, well she still enjoys hers at almost 10mths.
HTH
