The problem is that it is almost impossible to have a true ceteris paribus scenario with 9-yo computer gear. To stay with the 2014 OS, for security reasons you would need to have the box fully isolated from the internet for one thing. That usually is not feasible, and once you upgrade anything things change.
That said, you may well find your 2014 setup quite adequate once you put in a large enough, fast enough SSD as a boot drive and using the best available OS version. The folks at OWC can give you good advice on the upgrade.
It depends on how you use it along with the quality of your security skills and knowledge.