Lead-free tetragonal tungsten bronze Sr2LaTi2Nb3O15 ceramics were prepared and its crystal structure determined. Dielectric response of Sr2LaTi2Nb3O15 was investigated in a broad frequency (100 Hz–90 THz) and temperature range. The observed relaxor-like behavior can be generally described in the framework of polar nanocluster dynamics concept. However, some peculiarities in the dielectric response, relaxational, and crystal lattice dynamics (e.g., hardly resolved Vogel–Fulcher part of the relaxation, reduced dielectric strength of the cluster flipping mechanism, absence of ferroelectric phase under electric field, absence of the polar soft phonon, etc.) were revealed. Therefore, we claim that Sr2LaTi2Nb3O15 is more alike to dipolar glasses than lead-based perovskite relaxor ferroelectrics.