It may not happen today, but over time, we are going to start seeing more 15-2 upsets and probably even a 16-1 upset.
Beginning last year there are now six #16 seeds, when there used to be just four, and then five for a while. At the bottom of the bracket, there is a bigger talent gap between teams, meaning that the sixth-worst team in the field is quite a bit better than the fourth-worst team and is much more likely to upset a #1 seed. That also means that the tenth-worst team is now a #15 seed instead of a #14, and is much more likely to knock off a #2 seed.
You mention Lehigh as an example. They are #82 in the Pomeroy ratings. Virginia Tech is #83 and they lost to Duke 3 times by 4-5 points each time.