1d sofa with the s from seat and the ofa from of authority
15a degree as one degree out of 360 is not much of a turn
I agree these are "thin" but nothing else works in the case of 15a
K-
I take it that you disagree with the choice of sofa. You prefer safe? Why?
My reading of the definition of seat in Chambers is seat is "a post of authority." Thus the clue itself is tautologic.
Given the ST's history of sloppy editing, I'm inclined to think the clue is supposed to read "personS of authority" making SOFA the answer. I just can't see SEAT.