I am familiar with this poem.
I don't know where it originated but I came across it last year on a different web site with exactly the same introductory and final comments.
I enjoy it a lot although I have some reservations about it. I honestly believe that far less than 90% of native English speakers could correctly pronounce every word. This is due in part to the inclusion of a number of characters from Greek mythology and a few words verging on the obsolete, not to mention those with more than one accepted pronunciation.
Another problem with it is the fact that not all native English speakers speak with the same accent. I speak RP and I imagine that the rhymes work best with that form of pronunciation, but perhaps that's not so.
Nevertheless, anyone with an education should be able to manage most of it, and it is a lot of fun.