Lexus Drivers web page has this posted

Version 16.1 is the newest map update available for purchase from your Lexus dealer for any Lexus vehicle using GEN6 and higher hardware. It was released Fall 2017.

I'm about to take my car in for its 60K Service. Was thinking about updating my Navigation since its never been updated.

Lexus didn't come out with a Fall of 2018 Update?

 

Looks like they did. Part number seems to be PT219-GEN08-18. Here's a link for reference but I'd double check with your local dealership parts dept:

https://www.lexuspartsnow.com/parts/...-gen08-18.html

According to the Lexus owners page the 2015 IS250 has a gen 8 unit. Link to Lexus help page