EstimatedPartitionCount / EstimatedRowCount / SnapshotSize seem particularly expensive. For example on our system org.apache.cassandra.metrics:type=ColumnFamily,name=SnapshotsSize can take as much as half a second.
All this cumulated means that export stats for all your tables (with metrics-graphite or jmx_exporter) is going to take quite some time.
We should certainly try to find the most expensive end points and see if there is a way to cache some of the values.
cc: Romain GERARD