ABS tends to break down faster than pla.
Pla is also a lot harder and more durable.
When 3d printed :-)

There are several filaments that can be 'smoothed' rather than polished.
To 'polish' you'd just paint it with a clear lacquer - which would probably help make it last longer.

As far as pla breaking down in 15 years.
I'm not even sure if there were any 3d printer pla filament around 15 years ago - so doubt there are any cases to look at :-)

polymaker do a pla based filament that can be smoothed and made shiny.
https://eu.polymaker.com/product/polysmooth/

And you can do the same thing with abs and a box filled with acetone fumes.

If you want to invest in a decent machine - then some of the really hi-end plastics like PEEK - which are often used instead of metals - would become a possibility so I'm guessing their useage lifespan is pretty long.

Polycarbonate is printable with a decent hotend and some experimentation - that's about the toughest material a 'standard' fdm machine can handle.
And then there's always nylon - again you should be able to make it shiny with the right coating.

But for things like polycarbonate, nylon and abs - you will need a heated enclosure.
Of the creality machines - Pretty much only the ender 5 is easy to enclose.

I'm not a fan of the creality price over practicality approach.

What I'd say is have a look at some of the new corexy printers.
Easy to enclose, great quality and speed and very easy to put together - and there are a few around the $300 mark as well.