I'm about to check out a 2015 Lexus RX350, and just by doing a quick AI search looks like 2015 is a safe bet and considered one of the most reliable? Is it safe to assume that? Any known issues on this specific model that I need to look out for when checking a prospective car that I'm gonna purchase?

 

Check for water in the side recesses of the trunk.

 

oh, is there a known issue with leaks? is it coming from the roof?

 

It’s the same problem as on the second-generation Lexus RX (I owned three of them, and all of them had leaks in the trunk, regardless of mileage).
There is a lot of information on the internet regarding all potential leak points.