Low fps in the user perspective

Hi everyone! (Sorry if I’m writing in the wrong section, this is my first post here.) I’m having a problem with Blender (2.70). I can’t work in the ‘‘user perspective’’ because I get, like,1 frame per second when I open a mesh (in this case from The Sims 4). Can someone help me?

My PC config.: Intel Pentium G3240 - 3.10GHz / 4GB Ram / GTX 750