The ketohexose shown is described by (i) its family (D or L, from the highest-numbered stereocentre) and (ii) the number of stereoisomers of its constitution (configurational, open chain). Which pair is correct?

The highest-numbered stereocentre is C-5, which is S here; D-sugars have R at C-5 (as in D-fructose), so this sugar is L-sorbose, an L-series ketohexose. A 2-ketohexose has stereocentres at C-3, C-4 and C-5 only, so there are $2^3=8$ stereoisomers (verified by RDKit), not 16.