No offense, but I think 2:49 is overly aggressive as well. I would not rule out the possibility of 2:49 or 2:45 in future training cycles, but times don't drop quite as fast later on as they do early on. So a lot really depends on your running history - if you were a 17:00 5000m runner at some point in the past, that would be good to know. If you just started running a few years ago, that would be good to know. But it would all still be a guess.
In any event, I hope my assessment is wrong and you kill it.
No worries, it absolutely makes sense.
Last year, on 1st July on a 10k I couldn't even manage to break 40 minutes, but on 1st October (14 weeks later), I ran a 2:59 marathon without any issues.
Usually I am far better on long distances, that is what gives me hope.