I noticed the same thing and intended on calling the parks dept this afternoon. It wasn't just between 14 and 15, the whole course was littered with their water bottles and baby Gatorade bottles and snack bar wrappers. It was definitely the jerks from the race.
I meant to look at the sign which was posted on the kiosk at hole one, as it was still up when I played on Saturday afternoon. I forgot after becoming more interested in a guy that was all over the back 9 with a maul, hacking through the grasslands and the woods... looking for discs. He told me, "Oh, I'm just out looking for a whole bunch of discs I lost out here over the course of the week... I lost about 10 of them and I decided I should come back up and look today." His whole story sounded kinda fishy and left my group with the distinct feeling that he was just cashing in on others misfortune.
Anyhow, I picked up as much as I could fit into two grocery bags... but that didn't begin to put a dent in it. I'll call the parks people and report it. I encourage as many disc golfers as saw this to do the same. If we don't report it, everyone is going assume that it's the golfers leaving the mess.
EDIT: I just contacted the parks dept AND sent an email to all of the event organizers and the superintents at Hazelwood Schools. They are the ones who hosted the race - I found the info here: http://www.athletic.net/CrossCountry/Results/Meet.aspx?Meet=58400