Hi,
To be part of the beta, you;ll need to pm me with a gmail address, we'll add you to the group.
serialization is dependant on what you serialize, so in order to be able to do anything here, we need a repro or more information. in your case, since it's linked to prefab youc an create a dummy scene that will load up each prefab one at a time, and then you can check which one takes the most perfs out and then check what data is in its fsms. and cut them down until you find which ones are most impacting, this will help a great deal to know exactly what's going on and take appropriate steps.
also, it goes without saying,but you should be using a pool manager, if you do, are you sure it's setup properly, this should improve this kind of performance impact by having already instancitiated a set of prefabs in the pool before it actually starts running.
Bye,
Jean