Denise - I completely agree with your friend. I would NOT do the run today. Just from personal experience - I was coughing pretty bad a few winters ago, had some stuff coming up but not major - and had a half marathon I wanted to do. My dh warned me, he said you should NOT do it, you'll pull it into your lungs. Did I listen? Nope. I ended up with pneumonia and it lasted for 2 months. It was so bad they wouldn't let me do anything - no running, no nothing - not even yoga. It sucked and after all your hard work, I don't want to see anything like that happen to you.
You have done all the work leading up to this week. You've swum, rode and run your heart out. Your body is telling you it needs a rest and I really think you should listen to it. If you give yourself a few days to get rid of this stuff, you can get right back on track next week. I know you're going to be tapering, but - girlfriend - you KNOW you can run 15 miles. You've done it before! Don't risk making the infection you have worse - let it heal up and you'll come back strong for IMAZ.
Rest!!
M