Hope he's ok 
We have a Springer puppy who is 6 months old. He's currently 12.7kg and going to be a little one, breed average for males is 20-30kg. 30kg would be a big Springer I think.
No expert but wondered a couple of things. Could you do 2 x 30 minute walks a day therefore increasing his exercise but not the exercise load?
Small caveat - our puppy gets bags of exercise, an hour in the morning and about 75 minutes in the afternoon. Our vet is fine with this because he just potters around me and rarely goes more than half a field away at most, he's more of a sniffer and would rather hunt out poo to eat than chase a ball! She did warn against repetitive ball throwing, as this is wearing on the joints, but I do appreciate your dog is fully grown though but just thought I would mention.
The quality of kibble varies greatly, I researched this a lot before getting out puppy, although he's now moving to a raw diet anyway! I can point you in the direct of a couple of good websites for food but it's quite an eye opener what fillers some brands use, including the popular ones.
Ours has Taste of the Wild kibble, which is grain free but expensive, in the morning and we will move to raw completely when our supplies are used. You will be surprised when you weigh out the appropriate amount for an ideal weight adult how little there is!
In the evening, a bone or a couple of chicken wings, a drumstick or thigh. Sometimes some oxtail. I get a lot from our local farm shop, including the bones which I get free but last week I bought a bag of Sainsburys savers frozen chicken pieces (various pieces, drumsticks, thighs, wings etc) for £4. That will last a while. So, raw feeding doesn't have to be a chore but, yes, it's a bit more work than a bag of kibble.