How long is a too long paragraph?

I've just heard from someone in a book group reporting that another member of that group, who are all to my joy reading my novel The Small Book, was dismayed by the length of the paragraphs in the first chapter - and by the density of the text. I've just looked at it again. I think the longest paragraph has 18 lines with around 11 words to a line. Is that off-puttingly dense? Opinions welcome.

Meanwhile, in Speak, Memory Nabokov's paragraphs are something else....as indeed is his writing. Dream on.