Our team has created its own minecraft launcher, where you can choose the optimal game settings suitable for the power of your computer:
How to use the Pixelmon Launcher.
Put the Launcher file in a folder and launch it.
Pixelmon needs 64bit java to be able to work, if you have problems running the modpack ensure you have a 64bit version of java, alternatively download java on java.com
Download the Offline (64bit) version.
Install Pixelmon by ATLauncher, Technic Launcher or by Manual Installation: