Bug when player join a scene with too many network behaviour

Hello
I’m working on a 5 players Multiplayer, Lan-only project
I got a very big scene, with a lot of network behaviour(20k-30k) that I need to keep sync. let’s say this is a big building, with 20.000 doors.

If the players are all theres before i spawn the doors it work nice, but if the players join the server after that, the server get an error :
ChannelBuffer buffer limit of 16 packets reached.

If I understand, the problem is, when the player come, he get the datas for every doors, and the server the server get saturated.

i’m using the standard Network manager.
What can I do ?
Can i set the network manager to send data more slowly ? The player could wait 5 seconds before the game start.

Or could I set a bigger Buffer ?
i have looked at :
http://docs.unity3d.com/ScriptReference/Networking.ChannelOption.MaxPendingBuffers.html
http://docs.unity3d.com/ScriptReference/Networking.NetworkConnection.SetChannelOption.html
(from this tread)
But i don’t understand how to use theses

Is there a good thing to do ?

It is for lan only, on 5 dedicated computers.

Did someone have an idea ?