Its achievable if you want it to be, but obviously that may mean 12 hours a week for you or just a couple. It also depends on your other commitments etc etc.
My inclination would be to go for it, isn't that the point of triathlons really? that it is a physical challenge? The nearer you get to the date the better your focus will be.
I entered the great london swim last year and until 2 weeks before I was resting every 200m. Then in the last week of training my brain understood that I had to swim a mile and my body and brain got together and I managed.
Sometimes we need to set time specific goals.
What do you have to lose, your entry fee if you have to quit before getting to the bike?
Chrissie Wellington only entered her first triathlon as part of a work challenge, having been an average squad sprint swimmer at university. She won that, entered and ironman a short time later and broke the world record so feed off that sort of inspiration. all the best.