I would tend to think the 8:45 3000 mark is easier than the 15 5000. But it depends on what you can deal with better--a faster pace or a longer distance. If you recently ran 4:40 off of minimal training at your age, with a sprinter training, I'd say shoot for the 3k.
I'm not going to say it's completely possible--the real unknown here is how much talent you truly have. While your 1500 result gives a small indication that you might be talented enough to do it, it really isn't a definite indicator. This all matters because at your age, you're going to be relying a lot on your genetic talent to get you through this. You don't have any significant training history and your body is definitely past its peak.
But, if you are talented enough to do it, I would say there is a chance. You will definitely need to start training ASAP--the longer and more consistent your training is from now until race day, the better chance you have.
I would also suggest you try to find another fast track that World Athletics picks up results from, and plan on racing to hit this mark at least a couple of times. IMO, you are giving yourself a better chance the more times you race.