The recommended value for the output capacitor is 22uF. The architecture of the TPS6215xA-Q1 allows the use of tiny ceramic output capacitors with low equivalent series resistance (ESR). These capacitors provide low output voltage ripple and are recommended. To keep its low resistance up to high frequencies and to get narrow capacitance variation with temperature, it's recommended to use an X7R or X5R dielectric. Using a higher value can have some advantages like smaller voltage ripple and a tighter DC output accuracy in Power Save Mode (see SLVA463).
Note: In power save mode, the output voltage ripple depends on the output capacitance, its ESR and the peak inductor current. Using ceramic capacitors provides small ESR and low ripple.