I've been working through a bit of this in another place.
In no particular order: 1 is Chinese years; 9 is colours of the rainbow with respect to the poems of Tennyson; 12 is tennisists; 5a is cheeses; 3c is Sylvesters; 2a is probably New Horizons; 3a is 'great'; 15 is indeed 8, or 9 if you're being really picky; 4a is Marilyn Monroe references; and 14 is possibly birthplaces and kingdoms of a variety of monarchs.
Enough to get you started?
by Cedric Lackpot, in response to this post 2015-12-10 21:03:08