1.5x increase in incremental build time only for PLASMA 1000, 10k Index Tests

For the test : 

Incremental index (min), 1 bucket x 50M x 1KB, 1000 indexes, 100K KV ops/sec, no mutations during initial build only, Plasma, s=1 c=100 

5017 - http://perf.jenkins.couchbase.com/job/hemera/1566/ - 10.8 mins
5075 - http://perf.jenkins.couchbase.com/job/hemera/1697/  16.7mins
 
Seeing the same pattern in 10k Index Test 
 
5017 - http://perf.jenkins.couchbase.com/job/hemera/1567/ - 19mins
5075 - http://perf.jenkins.couchbase.com/job/hemera/1698/   23.8 mins

Stats Comparison : 

http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=hemera_700-5017_build_incrindex_8415&snapshot=hemera_700-5075_build_incrindex_5125 

Changelog : 

http://changelog.build.couchbase.com/?product=couchbase-server&fromVersion=7.0.0&fromBuild=5017&toVersion=7.0.0&toBuild=5075&f_analytics-dcp-client=off&f_asterixdb=off&f_backup=off&f_build=off&f_cbas=off&f_cbas-core=off&f_cbas-ui=off&f_cbbs=off&f_cbft=off&f_cbgt=off&f_chronicle=off&f_couchstore=off&f_eventing=off&f_eventing-ee=off&f_goxdcr=off&f_indexing=on&f_jsonparser=off&f_kv_engine=off&f_libcouchbase=off&f_magma=off&f_ns_server=off&f_phosphor=off&f_plasma=on&f_platform=off&f_product-metadata=off&f_query=off&f_query-ui=off&f_testrunner=off&f_tlm=off