The second phase of H. E. S. S. is being commissioned and will start physics data-taking in Autumn 2012. The 4-telescope configuration is now enriched with a new very-large Cherenkov telescope (VLCT) at the centre of the array. The similar to 600m(2) mirror area and high-resolution camera of the VLCT will permit to lower the energy threshold to about 30GeV in the single-telescope mode, opening a new observational window to a large number of new high-energy phenomena. Adding the VLCT also enhances the detection sensitivity in the multi-telescope mode. The performance in this latter data-taking mode of HESS-II with the advanced analysis procedure called Paris-MVA has been studied in order to understand the achievable low-energy sensitivity and preliminary results are shown here. The Monte Carlo (MC) simulations, the gamma-ray reconstruction procedures and the analysis strategy used to obtain the resulting improvement in sensitivity by adding the VLCT - of about a factor of similar to 2 at low energy - will be discussed.