16) 'apocalyptic horseman' is def of 6 letter word. 'somewhere in London' is def of 12 letter answer
17) This is the thematic answer
18) 'embryonic' is def of 6 letter word. 'China' is def of the 12 letter answer
19) 'handles' is def of 6 letter word. 'Supplier of sensational info' is def of 12 letter answer.
Still can't get 15.
Let me know if you want stronger hints about the wordplay.