Is the 2015 CHEVY SILVERADO 3500HD a good tow rig

I agree with the Chevy. It's funny because I find that my Chevy is much more comfortable than the other two. I did have a Dodge and the motor was great just the ride was very hard.
I've pulled my rig from Lousiana to Cali., from Louisiana to Nebraska and all stops in between and it has preformed great. My only complaint is the fuel tank size in my 09.
But like the others have said its preference, It's what you like.

Love my 2015 Silverado. Engine is bullet proof imo.
My 2008 is just as good. Only complaint I have is mileage due to the exhaust recycle. I traded a Dodge dually for it. Dodge had a decent motor, although noisey. Seats were hard and flat. I drive the duallys a lot so they need to be comfortable.
My father tried a 2012 Ford and traded after one year. Ride and seats were rock hard. Mom couldn't handle the rough ride. It was new and traded for a used duramax and couldn't be happier.
Pick whatever you like and have the most knowledge of.

Love my '08 GMC 3500. Zero issues in 124000 miles. Agree the seats in a Ram are more comfortable. Disagree with engine quality. Ford has had two engines with more problems 6.0 and the 6.4. Any vehicle can be a lemon that what the warranty is for. Drive all three and whatever feels the most comfortable is the one to go with.

As a person who has owned all of the big 3 I am going to take a different tack on answering your question as you have not provided extensive information.

When it comes to diesels Dodge has the most bulletproof system, then Ford and then GM. GM is making headway, but has not got all the quirks worked out yet. As for gasoline powered vehicles there is no one vehicle that stands out above the rest. Each has its strong performers and its lemons.

Really what it is going to boil down to is what pleases you. For example, I have found that the seats in GM vehicles for the past 20 years are very uncomfortable to sit on so I stay away from GM for that reason and go with Dodge or Ford.

There are your diehards like my BIL who will only own a Dodge and my son who will only own a Ford. Me? I drive each every time I go looking and usually end up with the same conclusion Dodge or Ford for comfort reasons and purchase from which ever dealership gives me the biggest discount on the vehicle I desire. And I will shop every dealership in a 100 mile direction, and I have had prices vary as high as $1500 on the same truck (Ford to Ford & Dodge to Dodge)