It appears the Driver's Seat Memory feature is exclusive to the Comfort Package.
Therefore, I'm assuming, it seems unlikely to be included with the Premium Package...even though the Premium Package is more expensive.
I think the Comfort Package is included in the Premium Package but I would ask your salesman to find out. If you build a 2016 NX 200t AWD on the web site and select the Comfort Package then add the Premium Package it will remove the Comfort Package.
I purchased a 2015 NX 200t F-Sport and the Comfort Package came with the Premium Package and at that time the Comfort Package was an individual option. My window stick doesn't show the Comfort Package as an option but does list the contents of the Comfort Package on the windows sticker.
What Cyber Dude said. I have the Premium package in my 2016 NX & it has all the Comfort package stuff w/ it, including memory seating set for 3 drivers. When I discussed building a vehicle on the Lexus website as compared to the vehicle they sold me, it never would come up the same as the sticker! They said they hear that a lot! They tell Lexus all the time & they said that Lexus has told them they are "working on it"!