Hello, I do not like the keyboard and if I end up buying the MBP 2018 and when something with a better keyboard comes out in 2-3 years, about how much can I get back through the Apple's trade-in program? Half? 1/3?
Go to their trade in program and simulate trading in a 2015 MBP and compare that to the original price of it. It will likely be close to what you'll get (percentage wise) in 3 years for a new one.