Stability of hexakaidecahedral clusters in the presence of guest molecules like Ne, N-2, CH4, and C2H6 molecules are examined by first optimizing geometry at the Hartree-Fock (HF) level with the 6-31G* basis set followed by a single point energy calculation at the MP2 level (second-order Moller-Plesset perturbation) and using the same basis set. For N-2 and CH4 molecules, both the single and double occupancy of the cage cavity have been examined. In each case the cluster with single occupancy is more stable than that with the double occupancy, and contradicts an earlier simulation result. Even when the guest molecules are small enough to fit into the cage cavity, there seems to be an optimum size of guest molecules at which maximum amount of stabilization is achieved.