Are you on WiFi or 3G? 3G speeds will depend on the strength of the connection in your area.
WiFi should be much faster.
Have you tried a reboot? Charge it, unplug it, press and hold power a full 30 to 40 seconds, then release power and let it reset.
Is your software up to date? It should be
version 5.8.9.2.
How many books are on the device? More than a few hundred can cause significant slowdowns of some processes.
You might need to contact
Kindle Support if it is still having problems.