For someone who hasn't opened the app in three years going through the upgrading process for each major version/minor high version would be more difficult vs rewriting for most smaller components.
To the parent's parent's point Javascript has evolved since 2015 and comparing what a 2015 app looks like to a 2018 app is day and night.
To the parent's parent's point Javascript has evolved since 2015 and comparing what a 2015 app looks like to a 2018 app is day and night.