At 7500km you can replace the chain only. I know, I know... always replace chain and sprockets together because old sprockets will prematurely wear a new chain.
If you buy a quality new chain and keep it lubed, you'll most likely get near 20,000 miles (not km's) from it with your barely worn sprockets.
And the big plus is it's easy. Thread the new chain using the old one as a snake, rivet the link, adjust for slack and you're done.
Replace them all as a group next time.