Sorry this series uses a different interface for the AirPort board than the newer unibody and early retina systems as you can see here
[product|IF161-090] and [product|IF162-019]
Whereas the the 2012 15” uses a single combo bd [product|IF161-083] to get to handoff services.
And to get to AC WiFI you would need to jump to [product|IF123-048]
As you can see between the physical boards being very different in size the interface is also very different it just physically can’t fit. Lastly, the limitations of the OS your system is limited to won’t offer the needed firmware or drivers to support it.
Yes it’s a bummer! I finally had to give up on my 17” systems years ago because of the slow WIFI too.