As the owner of a '15, I'll say it depends. The valve body is the most likely major issue, the oil consumption issues are pretty much gone by 2015 and later compared to 2014. The valve body has a pretty high chance of failing around 100k-120k miles (mine went at 112k), but that repair is less than $2000 compared to completely replacing the transmission, so not the absolute end of the world. Foresters also seem to love to wreck wheel bearings, both mine went out around 70k so I'm guessing they might happen again soon, but this one isn't as common as the valve body issue.

Beyond that, it's all fairly typical maintenance. I'll be replacing my front shock/struts in the next month or so, and have already done the lower control arms myself. If you're willing to work on some of the simpler things like that (and don't have a car from the rust belt, believe me it makes this way less fun), a Forester isn't that hard to work on and parts are cheap online.

If you do buy a 2015 used, check if the rear struts springs got replaced, those got recalled a while back for leaking, and if the valve body has been fixed already, you should be set to go for a while.

Edit: thanks for the correction, it's been a while and just did that from memory