Slow incremental indexing and view compaction on idle cluster

Workload:-
Phase1
Load 15M items, 1K value sized , wait for indexing and view compaction to complete,
It took about ~73 minutes to create the first index.
Phase2
Mutate 10M items, and change value size to 1.8K.
Wait for indexing and compaction to complete.
There is no front end load, the cluster is just doing view compaction.
The view compaction post initial building process is still going on. ~ 48hrs plus

1 ddoc with 4 views in each.
15M items, replica=1, replica_index=enabled.

1 ddocs, 4 views in each.
10.6.2.7:8091

Indexes and database files live separately, with dedicated disks.

Some disk benchmarks on index partition:-
https://friendpaste.com/1JxnXjI6YcsQtFLSAWqYa6
https://friendpaste.com/1JxnXjI6YcsQtFLSAWqXsO

node 7
8.5G /data2/@indexes/default/main_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.2
7.7G /data2/@indexes/default/replica_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.1
6.1G /data2/@indexes/default/replica_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.1.compact
257M /data2/@indexes/default/replica_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.log
20K /data2/@indexes/default/tmp_02dcc6636d5e6f2bb68fd0fc592ba9a0_main
16K /data2/@indexes/default/tmp_02dcc6636d5e6f2bb68fd0fc592ba9a0_replica

node 11
11G /data2/@indexes/default/main_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.1
8.9G /data2/@indexes/default/main_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.1.compact
565M /data2/@indexes/default/main_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.log
8.8G /data2/@indexes/default/replica_02dcc6636d5e6f2bb68fd0fc592ba9a0.view.1
20K /data2/@indexes/default/tmp_02dcc6636d5e6f2bb68fd0fc592ba9a0_main
20K /data2/@indexes/default/tmp_02dcc6636d5e6f2bb68fd0fc592ba9a0_replica