The coupling between surface plasmon polaritons and confined acoustic vibrations in embedded silver nanoparticles is studied both theoretically and experimentally. The inelastic light scattering spectra simulated assuming deformation potential and surface orientation mechanisms are quantitatively compared to Raman measurements. The effects of size distribution width and profile and excitation energy on the low-frequency Raman spectra are addressed in this work and used to provide a characterization tool of the size distribution of metal nanoparticles. The quantitative agreement between measured and simulated spectra supports the fact that the surface orientation mechanism gives the dominant contribution to the resonant Raman scattering mediated by surface plasmon polaritons.