Recycling a damaged Late 2015 into a late 2013 MBP Retina

Normally I work on pcs, not macs so I'm not real sure of my options but I'm trying to help a girl out.

She has two MBP, a late model 2013 (8GB Ram) and a late model 2015 (16GB Ram). The 2013 has a bad speaker and the keyboard has a few keys that no longer type but otherwise is in perfectly fine working order. She uses a wireless keyboard which she says "...is cumbersome to travel with."

The 2015 has seen better days, the case has more dents and dings than a golf ball and is acting up (powers off, the cooling fan is LOUD, battery only lasts 45 minutes, and missing a few screws from the bottom of the case so the touchpad doesn't always recognize taps, and there are two lines going horizontal on the retina display).

She wants to know if the processor, ram, and keyboard from the 2015 could be moved to the 2013 laptop or would the performance be marginal between these two systems?

Generally speaking no.

Most Mac laptops before the last couple of generations could only upgrade the RAM. Some you could upgrade the storage with a different drive or SSD module.

I know, heresy, to most Windows PC technicians but the fact is all current generation Mac laptops have zero upgradable parts. No RAM, No HD/SSD, no Processor, GPU or anything else. It's all integrated to the system board. And replacement means you have a talent for replacing surface mounted parts.

You can get info on what is what on the Macs in front of you at the excellent

https://everymac.com

They have all the specs for all the Macs down to whether or not you can replace, RAM, HD/SSD, GPU, etc.

And for a good place to find out how to replace/repair those bits that are repairable/replaceable, there is the wonderful

https://www.ifixit.com

With lots of pictures and HowTos on replacing and repairing a whole raft of Macs and other Apple Devices, not to mention lots of other computer equipment and electronic devices.

Some of what you want to do may be possible. Keyboards may be the same or similar and RAM and Storage/SSD/HD might be compatible or close enough to do some of what you want. Those two resources should start you on the way of discovering what, exactly, you can and can't mix and match with those two Macs.