It's actually 1/4 mile swimming (not .4 miles), 15 miles of biking, and 3 miles of running.
My first day of swimming, I swam to the end of the pool and had to hang on the side and gasp for breath for several minutes before I could even do the breaststroke back. Now I can swim a half mile. I swam 1/4 mile this morning in about 12 minutes. That's in a pool, and I haven't done any open water swimming yet, but I'm feeling really confident that the swim should be no problem. (If you need to rest during the swim, you're allowed to grab a buoy so long as you don't use it to assist yourself in making forward progress. Also, I find the elementary backstroke very restful.)
I also feel pretty good about the biking. Part of why I decided I could do this was that I looked at the distances in January and thought, "I could go bike fifteen miles right now. I don't even need to train to do that." And, in fact, on January 10th, the weather was really nice and I biked almost 19 miles. (Admittedly, around mile 18, I really wished I could be at home RIGHT NOW but the first 15 miles were really no problem at all.) Yesterday, I went biking and rode 15 miles in 1 hours 22 minutes. Now, I ride a comfort-model bike, with extremely thick tires and handlebars that put me sitting up; I tried out haddayr's slick commuter model with skinnier tires and lower handlebars and was instantly much, much faster. I am pretty sure I could significantly improve my time on the bike ride simply by getting a road bike, and I may browse the Hub's Bike Extravaganza in June to see if they have anything I like for a good price.
Then there's the run.
Apparently most triathlete wannabes come in from running, and find the swimming part really intimidating, or occasionally the biking, but the running is a piece of cake, which is convenient for them since it comes LAST. I am not a runner, and I've never been a runner. I've spent a lot of the last few months trying to be a runner, and on my very best days I average MAYBE a 13 minute 40 second mile and go a little over two miles. Most of that, I'm walking rather than running. My knees have been doing OK, but running has been seriously messing up the right side of my lower back, and prompt icing helps but not as much as not running in the first place does. I saw my chiropractor and I took some time off to see if that would get it to heal and I may try again tomorrow and see what happens.
I tried my very first double-workout the day before yesterday: after my 15 mile bike ride, I put my bike in the garage and attempted to run around the block. I almost fell down, first of all, and then I had to stop halfway around because I was completely out of air and had a horrible stitch in my side. (OK: perhaps next time, I should use my asthma inhaler when I get off the bike but before I run. It does seem to make a difference.)
My fallback: I can walk three miles in an hour. I'm pretty sure there are people who do exactly that in this triathlon, and I'll still get an official time. It won't be very impressive, though.
It's frustrating, though. I know so many people who seem to swear by the Couch to 5K plan. Admittedly, I have not followed the plan in detail but I've used a similar approach: alternating periods of walking with periods of running and tried to gradually increase the running and decrease the walking. And I've made progress, but I'm nowhere near the point of being able to run 3 miles without stopping, even slowly, even without a 15-mile bike ride first. And it's not like I actually came at this from the couch; I was not super fit, but I did have a basic level of fitness that was not completely pathetic.
(kristine_smith, I notice that in your last post you suggested orthotics. I wear Superfeet inserts, the green ones, which were recommended ages ago for knee pain. I wear shoes bought from a running store, although perhaps I should go back and ask for a new assessment and shoe recommendation. I have weird feet, and there are a lot of shoes out there that might work for my back or knees but don't work at all for my toes or ankles and I hate shoe shopping and it feels infuriatingly high-stakes because shoes never feel quite right until you break them in, but if you wear them for a week and they're just not going to work you can't return them and then you're out $200 because good running shoes are also really expensive. I know this brand is comfortable for walking in, at least, even though they wear through at the toe in about two weeks...so I'm reluctant to switch.)