A Big Ten team (sorry, I won't say the name) took a walk-on junior who ran 15:49 in a road 5K, 4:32 mile. He worked his way down to a 4:20 mile and low 15's on the road by the team he was done. He always was the second or third to last runner on the team in XC meets, getting beat by freshmen.
I find that if you are low-16's, likable, have a really good attitude (college coaches hate whiners and wishy-washy types) and work extremely hard...you might find yourself on the roster of a team from a major conference. Another thing that might work in your advantage is having a few guys quit the team and having a spot open for you to jump into.