\(n_{KMnO_4}=\dfrac{15,8}{39+55+16\cdot4}=0,1\left(mol\right)\\ PTHH\left(1\right):2KMnO_4\rightarrow^{\left(t^o\right)}K_2MnO_4+MnO_2+O_2\\ \Rightarrow n_{O_2}=\dfrac{1}{2}n_{KMnO_4}=0,05\left(mol\right)\\ PTHH\left(2\right):S+O_2\rightarrow SO_2\\ \Rightarrow n_S=n_{O_2}=0,05\left(mol\right)\\ \Rightarrow m_S=0,05\cdot32=1,6\left(g\right)\)