2015 15" MacBook Pro (R9 M370X) [4th,4C,H] + GTX 1080 Ti @ 16Gbps-TB2>TB3 (Razer Core X) + Win10  

System specs

15"  MacBook Pro  Retina (Mid2015):

Processor 2.8 GHz Quad-Core Intel Core i7 (I7-4980HQ)

Memory 16 GB 1600 MHz DDR3

iGPU: Intel Iris Pro 1536 MB

dGPU: AMD Radeon R9 M370X 2 GB

Win 10 Home: 1903 18362.295

eGPU hardware

Razer Core X + Nvidia GTX 1080 Ti

Thunderbolt 3 to Thunderbolt 2 Adapter

Thunderbolt 2 Cable (2m)

External Monitor: LG 34wn80c-b

Hardware pictures 

Installation steps

Install Windows 10 - 1903 18362.295

Download latest DDU.

Reboot into safe mode.

Run  DDU  (remove GPU drivers for AMD). Then restart into normal Win10.

Install Nvidia drivers.

Create bootable apple_set_os.efi

Reboot with apple_set_os.efi, follow prompt and external monitor turned on.

Benchmarks 

CSGO about 200fps

Valorant about 100fps

Comments 

Unsure if it's important but I connected my thunderbolt cable closer to the charging port.

I originally tried to get my egpu running with an amd card (5700xt) but couldn't figure it out, constant errors such as error 12 and 43. Installed the nvidia card and it worked relatively easier comparatively. I was faced with error 31 but once I tried apple_set_os.efi it worked with no issues. Now I'm able to boot without apple_set_os.efi but still do so as user @macnexus suggests the laptop runs quieter and cooler when the dGPU is deactivated through apple_set_os.efi