I found that StartBehaviour(node_bt) is so slow although in async mode , is there any way i can save the graph instance in memory and simpliy copy it when using.
You could pre-instantiate the graphs (or the GraphOwner) at the start of the game and call StartBehaviour on them only when you want to use them. The option “On Start: Do Nothing” in the inspector of the GraphOwner is something that may help with this approach so that the behaviour does not start automatically when the GraphOwner is instantiated.