Most of the time, the slow render times are caused when you have 'Motion Blur' turned on. This setting can slow down previewing dramatically. Animation Composer turns on Motion Blur on the layer by default, so if you have not used this option before, it may seem the presets are slow.
To make your work faster, we recommend you to turn off motion blur on your composition when working and then enable it for the final render.
Here is how to enable/disable blur on layer/composition: