3.2.3 performance regression

We have optimized core queries to work with few nscanned and low ms. This optimization works in 2.6.11 and 2.4.9.

However, in 3.2.3 performance regressed badly.

In 2.6.11 we have,
"nscanned" : NumberInt(11),
"nscannedObjects" : NumberInt(10),
"keyUpdates" : NumberInt(0),
"numYield" : NumberInt(0),
"millis" : NumberInt(0)

In 3.2.3 we have,
"keysExamined" : NumberInt(10762703),
"docsExamined" : NumberInt(2208753),
"numYield" : NumberInt(84084),
"millis" : NumberInt(33272),

See the query, indexes, collection statistics and full profiler input in the attached document.

Note that the documents in the PostKey2 collection are similar to the documents described in SERVER-22872.