No running training

I had some friend invite me to do a Sprint triathlon with them in 2008.  I didn't have access to a pool and didn't own a bike.  So I just followed my favorite 1/2 marathon training plan for 4 months to and went and did the race.  

My friends were tired of my smoking them in all of our road race challenges so I figured that not training for the bike or swim would level the playing field a bit.  

There are all levels of preparation at races.  Some people will train for 6+ months at 10+ hours a week for a sprint triathlon.  Others will show up on borrowed bikes with less than 5 km of swim training, less than 100 km of bike training, and less than 25k of run training.  Those that prepare better will get through the course faster and with more ease.  Everyone that is there can had fun though. 

If you can make it through the swim without drowning, sure, go to the race.

But really you should ask yourself what your goals are.

When you say your running pace is "4:05" what does that mean? How long are you doing that for? How hard does that pace feel for that distance? How hard was the ride before? Just 100k of zone 2 easy riding or are you doing and hour of threshold intervals during that?

A better question would be what is your open 5k or 10k pace?

No matter the answer to that question, it is obvious that you would do a lot better if you were running three times a week.

How often are you swimming?