Just as an FYI: On my 1991 Q6 I had the same dreaded "15-year" neck relief issue, which, as has been said in the forum a number of times, is owing to the phenolic fretboard shrinking over time, not to the graphite composite. I would imagine that the contraction of the fretboard material gives the neck its backbow over time, kind of like geological forces wearing down stone.
Anyhow, I sent my neck to Jerry Dorsch at Graphite Guitars (he was formerly with Modulus), and he replaced the fretboard with a piece of phenowood he got from Zon. He also installed a truss rod, which is key because you always want the ability to make even the smallest adjustments. The tradeoff is that the neck is slightly thicker, because the original phenolic was super thin, so much so that it couldn't be planed level because there wouldn't be enough material left to install frets.
In any event, you said the neck relief is okay at this stage, but if it ever gets worse, you might consider surgery.