Mongodb incremental oplog Dump not working
You are essentially attempting to dump the entire oplog and hence paging in all of it, not just the most recent data.  That is going to cause a lot of IO, especially when your oplog is too large to fit into memory.  On a smaller database it's not a problem because the oplog is relatively small.

The reason why it's dumping the full table is because I believe you are missing some zeroes at the end of your time:

&gt; new Date(1452157469)
ISODate("1970-01-17T19:22:37.469Z")


I assume you wanted this:

&gt; new Date(1452157469000)
ISODate("2016-01-07T09:04:29Z")


The speed this dump happens will depend on a number of factors, but mostly it will depend on how much data has been inserted into the oplog recently and how much of it is still in memory when you start the dump.