  Dielectronic recombination (DR) of Na-like Fe$^{15+}$ forming Mg-like
Fe$^{14+}$ via excitation of a $2l$ core electron has been investigated. We
find that configuration interaction (CI) between DR resonances with different
captured electron principal quantum numbers $n$ can lead to a significant
reduction in resonance strengths for $n \geq 5$. Previous theoretical work for
this system has not considered this form of CI. Including it accounts for most
of the discrepancy between previous theoretical and experimental results.
