What to replace DnD with?

I'm apparently looking at some old version. That would be highly appreciated.

>The party is currently level 9.
...how?
I started with 3.5, switched to 4e halfway through and we went to, like... level 11 in two years.
And the 3.5 campaign I started at a much later date hit level 14 in even less time.

>something with simpler rules and definitely lighter combat encounters. And focus more on interpersonal stuff than just killing fodder-level enemies.
Sounds like a job for Apocalypse World. There is an official fantasy version of it (2e preview "Fallen Empires"), but it's a pretty big shift in tone. And magic is definitely nowhere near D&D. More like undefined psychic stuff that's as likely to fuck you over as it is to help you.
Keep it in mind in case you cause the world to end.

Oh, and you didn't mention the tier.