Well I thought I was going to breeze through this as I filled in the top half with nary a hesitation or a google. Well, I did have to check 13ac as I'd never heard of it. Then I struggled over the lower half and can't quite parse all of six of them including 26ac (I can't remember the abbreviation for ambassador - is it his excellency?).
Like you Chris, I'd never heard of 15d and I can't fully parse it. I also nearly got caught by 25ac trap like Brendan, but I was sure of the parsing for 18d. I still can't parse it along with 21ac, 24ac (do the first four letters really mean dog?), 17d, which seems to be a letter short. I didn't know an alternative latin version to 2d. (I nearly gave that one away.)
My FOI 11ac, LOI 24ac and COD 16ac, though I also liked 19ac, 5d and 23d.