Hmmm...I'm not sure I completely agree with your statement. Well first off, in terms of inflation, 150k 10-15 years ago is what 200k is worth now (ballpark) but that's not the point.
That's like saying...20 years ago you could have bought a condo in NYC for 200k but NOW, since that same condo is worth 800k, it's not worth it anymore (the prices I'm saying don't matter, its the principal haha). You have to look at everything relatively. Maybe 800k for that condo is a steal! Maybe 100k for a dental education was a good deal 10-15 years ago, but today, that number is 200k. You also have to look at the state of affairs 15 years ago. How advanced was their dental training back then? Facilities? Resources? What about job perspectives? Today, because of medical insurance, it's better to be a DDS than an MD... but was that the case 15 years ago? What degrees are more valuable now? 15 years ago you could've gotten a great job out of college (for sure) or even high school. Today, good paying jobs are hard to come by but generally dentists are still doing pretty well.