My first guess is that the video card simply can't process quickly enough to run the preview in real time. If so, then there isn't anything wrong.

Try setting the display style to a simpler mode.

The spherical buttons high and leftward are simpler/faster display modes; lower and rightward are slower but more accurate. I use the fourth one, hidden line, a lot - it shows mesh penetration for placing feet on floor, etc. Try previewing in hidden line. If it runs in real time, your problem is solved. You can return to textured shaded display mode when you're done checking the motion timing. If not, then you might try ball #2 (outline). If it still lags, then tick the skip frames button; skipping frames will often enable the GPU to keep up with playback speed.

If you find yourself encountering this problem a lot, then you may want to consider buying a more powerful video card.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5