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I have never seen this slow drift in ceramic caps, yet I have seen fast memory effect drift in S&H designs using high Dk ceramic capacitors in the 70's. So I have learnt that all ceramic caps have memory effects (except low Dk C0G/NP0's).  The capacitance also changes with DC voltage, so Ic= VdC/dt + CdV/dt has a longer time constant as the voltage decays with R. I think of it as a partial response of an [electric double layer effect](https://en.wikipedia.org/wiki/Double_layer_(surface_science)). Although it is not as noticeable as the memory effect of all electrolytics, both capacitors and batteries.  I am not referring to the nostalgia of NiCad batteries that need a full discharge to remember their full capacity, but the memory effect of the previous voltage after an impulse short circuit and how they slowly return from a much large RC time constant. 

Capacitors that seem to have no memory effect are low Dk like all the plastic types.  PTFE, Polyester, Polyurethane, etc.

I don't see the need for R2 to match R1 so C1 could be much smaller with a larger R2.

All the rest of your design sounds excellent.