The first question will be what you going to tow it with. If you have a truck already what is the payload. That is the first spec you going to hit way before you exceed towing capacity. You can check your payload capacity by opening your driver's door and checking the yellow sticker for max payload.
You will be able to tow large trailers than 5er since 5er put more weight on the back of your truck. At 15,000 GVWR 5er can easily put 3,375 pounds (22.5%) of payload in the back of your truck and as much as 3750 (25%) depending on floor plan. While a trailer at 10,000 pounds will put between 1000 and 1500 pounds (10% to 15%). You still have to account for the weight of people and stuff in your truck.
That Payload number will help us advise you on which TT or 5er you can handle.