Congratulations on your first EV!
There are a couple of different theories out there I'll try and highlight for you.
Set 80% maximum charge - A few users on this board will tell you to rarely charge above 80% state of charge. Lithium Ion batteries like to stay between 30-80% charge, so the longer you can keep them in there, the longer your batteries will last.
Set 90% maximum charge - Same logic as the 80% charge, but this counts for the fact that a 100% state of charge, is not actually 100%. The charger inside your car regulates how much electricity can get into your batteries to make sure that they won't overcharge. No one really knows how much VW is limiting your batteries, so 90% is a compromise between letting the computer do the thinking, and you trying to take care of your car.
Charge 100% every night - Let the computer handle the batteries for you, and just plug it in every night. You just trust the VW did a good job engineering the car and you trust the default settings that the VW engineers put on the charger to allow for the optimum balance between range and battery life longevity.
I personally subscribe the the last theory, but I also commute 40 miles a day, so I want to make sure I have a full charge when I leave for work (I have a 2016 e-golf with the smaller battery pack, EPA rated 83 miles). If you are driving 15 miles a day, you may want to just charge up to 80% or 90% every night.
At the end of the day, no one here has had their batteries fail, regardless of their charging habits. The oldest e-golf (2015) will be under warranty until ~2022 or 100k miles. Given how low mileage most e-golfs seem to accumulate, I imagine we won't here about many battery failures until then.
