It's quite hard choosing a pet.
If you can find a good place that sells guinea pigs, that is trusted, then maybe you could get a guinea pig?
Hamsters could live more than two years, but I'm guessing it's quite rare. Maybe you could get a hamster and then move on to a guinea pig maybe? If you didn't do a lot with your guinea pig in the 15 days you had it, I'd go for a hamster to get used to have a rodent for a while.