it sure is. And you have three months to train for it.
you are doing 5km now no problem, so next week bump that up to 10km - with walking as needed, and do that for a month. don't try to go further than that for the first month and see how you get on.
the first week will be hard. the second week will be just as hard, the third week will seem a bit easier and by the fourth week you'll be looking for some more challenge. And that's when you step it up another 5kms.