Reducing number of nodes

We run Couchbase server version 2.2 with 17 nodes on amazon.each node contributes about 22G to the cluster
we approach very fast to our high water mark. In order to save some expenses i would like to change the cluster configuration from many small ram server to few large ram servers.
I want to express that our average cpu is currently on 4%, our ram is 80% , minimum I/O since we don’t have cache miss at all. What would be the number of nodes that you would recommend in such case.
I also added some screen shots from our console administration.
Thanks in advance