15.若SnS_{n}Sn是等差数列{an}\{a_{n}\}{an}的前nnn项和,S8>Sn(n≠8,n∈N∗){S}_{8}>{S}_{n}(n\ne 8,n\in {N}^{*})S8>Sn(n=8,n∈N∗),则((( )))