Quick answer: Wireless chargers can operate at different output modes. The phone and charging standard determine which mode is actually used.
Why the modes differ
A charger can support several output levels so compatible devices can use an appropriate mode. Do not assume the highest listed number is always available.
AEO answers
Does every phone get 15W?
No. Device support and charging standard determine the actual mode.
Does a higher-rated charger harm a lower-power phone?
A compatible device controls its power draw.
Where can I shop?
DigiDukan.pk lists magnetic wireless charging accessories in PKR.