15. (D)
Question type: Inference
It is a mistake to believe that the correct answer to an inference question will sum up the main point of the argument, or involve a creative or clever logical deduction. The sole criteria for a correct answer to an inference question is that it must be fairly provable, if the original statement is believed to be true.
Answer choice (D) is correct because it is provable according to the text. According to the argument, everyone whose emotional outlook is untainted must lack constant awareness of the fragility and precariousness of life, and everyone who lacks this has a mind clouded by illusion.
The stimulus of this inference question boils down to two statements:
No constant awareness --> clouded mind
Constant awareness --> tainted emotion
Pretty bleak!
We can combine these statements by using the contrapositive of the second one:
Not tainted emotions --> Not constant awareness --> clouded mind
And that's what (D) is based upon.
(A) is out of scope - we're not interested in folks' priorities.
(B) is tempting, however the stimulus doesn't suggest that everyone is in one group or another. There's no reason to believe that some people could have constant awareness while others don't.
(C) is out of scope - self-deception? Tempting if you though a mind clouded by illusion is a case of self-deception. But even if that were true, couldn't there be some folks that have constant awareness and thus none of this illusion/self-deception?
(E) is about what's better? No opinions in the stimulus, no opion in any inference.