In order for HFSS to utilize all the cores, you must purchase the MP or HPC license from ANSYS. HFSS by default will only access one core for solving. Also, depending upon your setup, HFSS solver may be trying to grab more than 1.4GB though you are unaware of it. For example, if you enable the iterative solver it will be very efficient on RAM and time. However, since the iterative solver is not suitable for all meshes, HFSS may determine that the iterative solver is a poor choice for the solution and revert back to the direct solver to ensure accuracy. You will need to post your profile for more info!
Have Fun!