First off I don't recommend you using Feral Heart + since it hasn't been updated in ages and it's extremely buggy & glitchy and not managed. Stick to the regular Feral Heart it will give you less headaches. As for the lag issue try going to the game's main menu and clicking "options" then "video" and setting your rendering subsystem from OpenGL to Direct3D9. Also turn Water Reflection off and View Distance to 0.