Personally, for 4 people I'd get the bigger trailer. 3-4' is not a big deal and a couch to sit on for a rainy day may just save your sanity. Just make sure your truck has the capacity for family and stuff with enough payload left for the hitch load. The Bullet 272BHS is a little over 5,000# empty so when you add stuff for a family of 4 plus battery, propane and some water we'll say 6,000#. 15% of that is 900# of hitch. Don't know if that 2015 GMC is a 1500 or 2500.
Since you say you are a newbie, you need to look at more than the trailer tow rating for your truck. There is a difference between pulling a boat and a TT for example. The "box" of a TT make lots of wind drag.
Have fun and enjoy.