I filled over half the grid at the start of the month then got stuck and put it aside.
Returning to it (in the wee small hours of this morning), as always seems the case, I saw the solution to 14ac immediately which then gave me 15dn.
I spent a long time trying to work out the anagram fodder hidden by the three asterisks, with a few red herrings, but finally found the correct combination in the Wikipedia entry for the poem.
As is customary for me, I initially didn't look further than the image of the original published version, so I was a little perplexed by 7dn. I assume that the Harper's typesetter made an error by repeating a word in the last sentence, and that the version used here is the correct one.
Hats off to Qaos for a refreshing approach to clueing.