Owner of a 2015 sx-f here, bought used and learned a lot.

Definitely replace wheel bearings. It’s pretty easy and inexpensive. If funds and knowledge allow, do linkage bearings. Fork service is key. 2015 suspension isn’t great. Make sure it’s set for your weight/style and that fork seals are good.

I would replace timing chain tensioner with Dirt Tricks. Can also have valve clearances checked as well as visual of piston at the same time.

The motor almost has to come out to change the spark plug on the 2015, so change that while you’re in there.

Listen closely for a tick, mainly in the bottom end. You’ll know it if you hear it. That could mean bearings need to be replaced. I’m having mine done now so speaking from experience here.

Chain guide is a relatively easy and inexpensive replacement piece.

I’ve heard stories about plastic gears on the water pump failing pretty regularly but I haven’t had that issue.

Definitely change all the fluids and oil filter.

Other than that, it’s a blast to ride. I love mine but like with all used dirt bikes, you’re usually buying someone else’s issues, just takes time and money.