A field-induced magnetic entropy change under high pressure has been experimentally studied for the LaFe11.5 Si1.5 compound. High pressure causes a linear decrease of the Curie temperature from ~194 to ~88 K, corresponding to a variation of the pressure from ~0 to 1 GPa. Appropriate pressures enhance the magnetic entropy change significantly in the meantime depressing the Curie temperature. A spike-shaped peak, followed by a plateau with a width of ~20 K, of the entropy change emerges and grows rapidly with the increase of pressure, and its maximum value is 138 Jkg K, obtained under the pressure of 1 GPa for a field change of 0-5 T. The pressure effect is also obvious on the entropy plateau. It results in an increase of the plateau height from ~23.8 Jkg K, without pressure, to ~29 Jkg K, when the pressure is 0.45 GPa. These results demonstrate the effectiveness of high pressure in modifying the entropy of LaFe11.5 Si1.5.