We study the relationship between signatures of high redshift ionization in large-angle CMB polarization power spectra and features in the Planck 2015 data. Using a principal component (PC) ionization basis that is complete to the cosmic variance limit out to z_ max=30,40,50, we find a robust >95% CL preference for ionization at z>15 with no preference for z>40. This robustness originates from the ℓ∼ 10 region of the data which show high power relative to ℓ< 8 and result in a poor fit to a

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... ike model of reionization. Instead by allowing for high redshift reionization, the PCs provide a better fit by 2ΔlnL = 5-6. Due to a degeneracy in the ionization redshift response, this improved fit is due to a single aspect of the model: the ability to accommodate z>10 component to the ionization as we illustrate with a two-step reionization model. For this and other models that accommodate such a component, its presence is allowed and even favored; for models that do not, their poor fit reflects statistical or systematic fluctuations. These possibilities produce very different and testable predictions at ℓ∼ 15-20, as well as small but detectable differences at ℓ>30 that can further restrict the high redshift limit of reionization.