Bug Report!
Ok, so finally I've found the common denominator for our Media Pending issue, at least with any variation of H.264 footage we have (a project either all AVCHD original, or all MOV original, or all ClipWrapped AVCHD to MOV).
With Premiere CC 2015 (2015.0.2) if you have any medium sized project (in our context: 35 bins in icon view on second monitor, 60 gigs H.264 source footage) with multiple bins open and set to icon view, it takes 15 to 20 minutes for the Media Pending graphic to go away. Once the Media Pending graphic goes away, any clip loads immediately when I double-click, however initially footage appears and audio plays, but the video is frozen for just a few more minutes then everything is fine. The project behaves as I would expect, no issues. 15 to 20 minutes before I'm up and running, really?
IF I go to every bin and switch from icon to list view, save the project, close/re-open, then Media Pending appears only a matter of seconds before Premiere is up and running with no problems. We did not have this super-long Media Pending issue with Premiere CC 2014 and we were actually using an older 2010 MacPro back then.
Something has changed in how Premiere deals with H.264.
(My initial test with AVCHD originals did not included much footage and not all the bins were set to icon view. So my bad for not comparing apples to apples.)
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2015 MacPro, 3.7GHz quad-core with 10MB of L3 cache, 12GB (3x4GB) of 1866MHz DDR3 ECC, 512GB PCIe-based flash storage, Dual AMD FirePro D300 GPUs with 2GB of GDDR5 VRAM each. Premiere 2015.0.2 The latest Yosemite (10.10.5) with a thunderbolt Sonnet enclosure housing a Kona LHi, SeriTek eSATA and SCSI card. Five drive software RAID connected via eSATA.