Maybe do a quick once-over of all your intake hoses to make sure the clamps are tightened down well. If everything looks good there, perhaps the OEM filter (Denso made) for your application simply isn't the best for efficiency. If that's the case - you could always try a different brand just to see if it makes a difference. Wix/Napa Gold would be an easy option. Either way - I wouldn't say your silicon level is "bad" per-se for a 15k run... but it's not spectacular either. Definitely didn't effect your wear numbers though.
In regards to the oxidation... one major thing that is often overlooked, but CRITICAL to know in long OCI's, is the TAN (along with the TBN). The typical "rule" is that once the TAN crosses over the TBN, it's time to change the oil as the additives are no longer able to fully neutralize the acids. It's not a linear progression either... as once the TAN climbs above the TBN, things like oxidation will accelerate at a more and more rapid level. Provided your lab provides the test, next time you get a UOA pay the additional to get the TAN tested along with the TBN. That will give you better insight into the oil's true OCI limit for your application (versus the 15,000mi "guarantee" that the bottle says).
