Been there, done that and got the tattoo! Not too difficult if your aim is simply to finish. I managed sub 13 hours on an average of 9 hours training per week; if I can do it then I'm sure you can. Good luck and enjoy it.
My triathlon mate and rival did an Ironman 6 years back. Sub 13 hours also. His greatest relief is that he did not get the tatoo. When a 2 stone heavier fatso runs round the Hove Park 5k he does not want that tattoo on show. The cap and bag still make an appearance, however, whenever I am in any event...along with the words 'Of course you have never done an Ironman, have you?'