Sorry, when I initially replied I misinterpreted your comment about not rated enough as there not being enough feedback from previous owners.
Once I reread it I knew what you really meant but basically didn't have enough information to provide a useful response. I understand that the 115s is a load index rating, but I don't have those ratings memorized so I have no idea how many pounds that represents. Nor do I know what rating your original tires had, which would at least tell us if the new tires you are proposing are at least equivalent or better than what Ford specified for the truck from the factory.
To give you a complete and accurate answer to your question, in a perfect world, you would provide the readings from truck scales for your rig and trailer as normally loaded.
I assume you don't really need that kind of answer and you're just comparing tires working under the assumption that your GVWR and individual GAWR are not overloaded by such a small trailer.
So, I would ensure that the max load in pounds of these new tires is equal to or better than what the truck originally came with. You can also look at the loading sticker on your door jamb and make sure that 2 of these new tires can carry more than the axle rating of either the rear or front axle to ensure the axle will be the weak link rather than the tires.
If your truck handles your trailer well with the current tires then replace them with something that has an equal or higher load index rating.
Also, be careful not to arbitrarily jump up to a D or E Load Range tire if it is overkill for your situation without realizing that those higher load range tires are usually heavier than lower load range tires so they will kill your fuel mileage.