15 watt wireless fast charge can charge 50 watts. Charging process and discharge process are mutually reversible processes, which is essentially a thermodynamic equilibrium process. In order to ensure that the battery is always charged in a balanced state, the charging current through the battery should be as small as possible, for this reason, the ideal charging mode should be the external charging voltage equal to the electromotive force of the battery itself.
Yes, there is no impact, because the wireless charging power is downward compatible with low power, rather than upward compatible with high power.