This depends on two aspects of power, for example, 15W wireless charging represents the power of the mobile phone, calculated according to 80% efficiency, the charger power you need to use is greater than 18.75W, but the mobile phone you may be biased, the efficiency may be less than 80%, it is recommended to be equipped with a charger of more than 20W.
Protocol, Huawei's original 15W charging base generally supports Huawei's own FCP fast charge protocol, of course, there is a large probability that it also supports QC protocol, PD protocol, if it is supported, you can buy a QC protocol 24W (12V\/2A) charging head should be the most cost-effective.