-Grow time-window of rolling timed 24h automatic update check interval (use google or forums power search for this)
-What repositories you have enabled in Fapman?
--Disable ones that you think that you do not need
-Be specific on how it´s slow? What is slow?
--Is it slow on downloading stuff or is list scrolling slow or what is slow?
-Check log files of fapman (from up-menu)

And last but not least. Default App manager is slow. Nothing what you can do with it. Just don´t use it. We have Fapman that is much more advanced.

.edit
Also please remember that commands that Switch_ just introduced gives you THE fastest way of 1. updating repositorie lists 2. Upgrading already installed apps and 3. searching and then installing apps. For minimum "zero" level try those commands and if it still "feels" slow then there is nothing that you can do. Of course you can install apps without first refreshing repositories.

btw. To use search from CLI
apt-cache --names-only search <yourkeywordhere>
Does search from downloaded repository list and check keyword only from package name, otherwise it checks full description.