In our experience, women like to talk about feelings. In our experience, most men will do anything to avoid talking about feelings. This often presents a problem. In fact, her pushing for commitment might be a result of your unwillingness to talk about your feelings. If you don't want to rush (or even ease slowly) into wedded bliss, the best way to slow the march toward marching down the aisle is to talk about it. Discuss where you're at and how you feel, and agree to revisit the discussion down the road.
If you don't have commitment issues, then you may just have issues with this particular commitment, which is a different, more painful conversation.