An example of what I'm describing is:

Decision A: 5 years (after 15 already spent) = 75% chance of success

Decision B: 20 years (after 0 already spent) = 10% chance of success

In that scenario, Decision A (sticking with your current research) is more rational as long as your estimate of your chance of success is accurate. We know from the article that this is not true -- their estimates were wrong.

The sunk-cost fallacy would apply for something like:

Decision A: 20 years (after 15 already spent) = 10% chance of success

Decision B: 20 years (after 0 already spent) = 10% chance of success

Since both A and B have the same cost and same likelihood of success, you should not consider the time you've already spent. Most humans would, though.