Idle speculations.

So ... as sometimes happens when singing ... Del might have grabbed a note that was a 3rd or 5th above the note he was supposed to start on, i.e., singing harmony. And also been a little flat.

If you multiply a frequency by 1.5 you get a perfect 5th ... essentially what speeding up 1.5 times does. But Del would still be flat if he was flat on the harmony note to start with. So he'd have to be sped up a little more than 1.5. But it says "almost 1.5 times?"

But then how could the lyrics have fit into the arrangement even if the vocal was now in key?

Must be more to the story in some dusty closet in an abandoned recording studio.

Help! I've fallen up and can't get down!