Is the bottleneck your CPU or HD? Check in resource monitor.
If it's your HD, reencode your file to make it smaller.
If it's your CPU, try upgrading to PPRO CS6+ which includes mercury engine & enable it https://www.google.com/search?q=premiere%2Bmercury%2Bengine&ie=utf-8&oe=utf-8
or
https://www.google.com/search?q=premiere%2Bmercury%2Bengine+on+windows&ie=utf-8&oe=utf-8