https://support.apple.com/en-ca/HT201624
Vintage products are those that have not been manufactured for more than 5 and less than 7 years ago. Apple has discontinued hardware service for vintage products with the following exceptions:
Obsolete products are those that were discontinued more than 7 years ago.
The oldest Mac that can run Catalina is from 2012, which is vintage but not obsolete. IIRC, obsolete Macs no longer receive updates, vintages one always/often do (they do in this case- assuming you are keeping macOS up to date).
With that said, I would guess at support for the 2015 MacBook until ~2022. Because the 2017 model was only just discontinued, it could have support into 2026.