You need to determine what makes you lag. It is very hard to improve things without knowing what there is to improve.
There are 2 possibilities that I see at the moment :
1- The cpu is overloaded by airodump-ng and possibly other processes.
2- You are connecting via SSH through wifi and having both overloads the network.
htop can give you an overview of the running processes. If you see that airodump-ng takes all cpu then you can't really do anything about it. If there are other processes taking cpu, try to kill them if they are not absolutely essential.
Have you tried running airodump-ng without SSH?