A good quality mattress that you pay a lot for should easily last from 10 to 15 years before you'll need to replace the mattress.
In 10 to 15 years you'll likely want to replace the mattress anyway due to dust mites and other bodily fluids that collect on the mattress over those years.
15 years is a long time and after 15 years I'd want a new mattress and probably a whole new bedroom set as well anyway.
You can help extend the lifespan of your mattress by keeping it as clean as possible and using a waterproof mattress protector on the bed and then just wash the water proof mattress protector.