Most of the time the slowness is caused by low memory or even spyware/malware. Make sure that your system is cleaned of any malware or spyware.
Another option is that you have applications running in the background while you are doing this. shut down the other applications..
A bad harddrive or a full drive can also have this effect as well as outdated drivers for the motherboard controllers.
A lot of bad registry entries as well can slow you down.