Sunnytec:
You could do your own buck converter with a Zener diode, it will probably weight less. I believe it won't reach 15g
This might be an idea for bigger drones, but the drone I used does weigh 50g only (I cannot weigh now, see below, but amazon says item weight is 1.76 ounces).
The buck step down converter I use that is able to handle up to 12A does weigh 81g ...
With a buck converter attached to the drone, you would not need the thicker cables.
In case the buck converter would be 15g as you said it would be even heavier than the 12.8g of the lipo shipped with the drone. With the additional cable weight that might avoid drone take off due to overload.
I did order recently a 150W 12V (12.5A) mains adapter from Amazon which seemed to be a better fit than the 170W 20V (8.5A) laptop mains adapter because I am only interested in 3.7-4.2V in the end. Unfortunately on first connection to mains it gave a very loud bang and blowed the room fuse. I already got it retruned and refunded, waiting for the reorder to arrive.
Currently I cannot do experiments with that drone because I lost it in another tree while on a new search mission for the RC airplane:
https://www.raspberrypi.org/forums/viewtopic.php?f=43&t=190407&sid=25471160e58720b71f95f6da16519f57&start=25#p1333694
I like scotty101 comment on my postiong 
You are going to buy another drone, to find a drone that was lost while finding an RC aircraft.. Perhaps you need to stop flying near trees? :lol:
Anyway, new FPV Eachine E52 drone (only 20$ with free shipping during banggood super sale!) arrived and I already did first flight exercises. Camera FPV on android smartphone should find the lost RC drone in 5-10m high small group of trees and rescue with 7m long ladder. And hopefully later get better location of 20m height tree RC airplane location and probably help in rescue that as well.
These are three slowed down from 30fps to 6fps parts from >60 flights that showed the airplane. First airplane enters scene from top right to middle right hidden by leaves, then plane enters frame from middle top and leaves top left, and finally plane enters from middle top and leaves middle top: