I am talking from a practical sense, not a legal sense in that you may be over the ratings by a few hundred pounds. If it was me, I would pass. Nothing worse than to spend all your time on a trip dealing with vehicle issues. Can your truck pull it - maybe. Only way to know is to test it before getting on the road for a long trip. You are going to be close to or past the truck's capacity to carry the weight and pull it at a decent speed, especially if you hit a grade. Even with trailer brakes set correctly stopping will be a challenge. You don't have the exhaust brake like I have on the Duramax, which helps a great deal.
According to the 2015 Chevrolet towing guide the trailer GVWR is just above what the truck is rated for. Living quarters trailers are heavy but I doubt you will max it to the 14,400# GVWR even with 3 horses and tack, unless you are hauling warmbloods or draft horses. Take it to the scales and get an empty weight on the trailer. You should be able to determine the weight of the horses, tack, and supplies to get a gross weight. Don't forget to have the water tanks full when you weight the trailer. Every gallon will add 8.33#.
I agree there is not much V on the front so you will have to be careful backing or making turns or you are going to damage the cab and trailer. Our Sundowners had enough V that I could almost get it at 90 degrees if I needed to get in a tight spot with our 2017 GMC 2400HD Crew Cab and standard bed. That trailer and a standard bed will be a little more tricky. Again, test it before you hit the road.
I would also be worried that the kingpin weight is going to cause the truck to be overloaded for total weight and on the rear. Having a light front end is an issue driving. Your picture shows the truck GVWR at 9200# and the rear at 6200#. Living quarter trailers are tongue heavy. If the loaded trailer weights 12,000#, that would be a max of 3,000# kingpin weight (25%). I would bet that the kingpin weight would be at or over that, especially without the horses in the back to balance the load. If you only have a total of 3000# of weight the truck can carry, that doesn't leave room for passengers and fuel. Again, something to check before the trip.
"Fifth-wheel or gooseneck kingpin weight should be 15% to 25% of total loaded trailer weight. The addition of trailer kingpin weight cannot cause vehicle to exceed Rear Gross Axle Weight Rating (RGAWR) or Gross Vehicle Weight Rating (GVWR). These ratings can be found on the certification label located on the driver door or doorframe."