Try lowering the resolution of your PD7 preview screen until you get the clips split how you want. There's a lot of overhead in displaying the clips while you chop them up.

Do you have enough memory? Is your hard disk defragmented? Have you cleaned up the temp directories lately? Win8 64-bit Pro Retail
Intel i7-4770
16GB DDR3 1600 8-8-8-24
MSI Z87-G45 Motherboard
ASUS GTX 660 Direct CU II OC 2GB GPU
1 TB RAID 1 (mirrored) Drive Array
Several scratch drives for video, TMP, pagefile.

I tried lowering the resolution of the preview screen but that didn't help. I have 2gb of memory. I will try to defrag my HDD. I have cleaned up my temp directories recently.

This either sounds like a slow computer or a lot of programs running in the background of your machine.

Try turning off everything that is running in the background of your computer by shutting down everything that isn't critical in your "system tray." What I am referring to is all the little icons in the lower right hand corner. These programs start when you turn on your computer. Right click on each icon and shut it down.

The other thing could have to do with how much and what type of RAM you are using. Spitting video should be almost instantaneous, and if you have to wait 20 seconds for this to happen, you may not have enough memory, your computer may be slow, or you may have lots of spyware on your machine that needs to be cleared out.

What sort of computer setup do you have?