A model was presented for linear susceptibility in ladder-plus-Y configuration of double quantum dot system using density matrix theory and including spontaneously generated coherence of Λ-type system. Wetting layer and quantum dot inhomogeneity were considered in the calculations, which gives a practical description of double quantum dot structures well. With increasing spontaneously generated coherence from Λ-component, the dispersion was increased and shifted under spontaneously generated coherence. The inclusion of wetting layer under spontaneously generated coherence increases gain which coincides with the published results. A possibility of slow light was predicted.