Let \( S_n \) denote the sum of the first \( n \) terms of an arithmetic progression. If \( S_{10} = 390 \) and the ratio of the tenth and the fifth terms is \( 15 : 7 \), then \( S_{15} - S_{5} \) is equal to:
\( 790 \)
\( 690 \)
\( 800 \)
\( 890 \)