Can trailer tires cause trailer sway? I have a 2015 jayco 26bh and I am sure the hitch is setup correctly, but I am getting more sway than I would like. When a semi or a truck pass by it really pulls ...
Most likely you have Passenger tires on the truck and not LT tires. The LT tires will make a huge difference.
Put Goodyear Endurance tires on the trailer. The only ST205/75R15 GY has is a D load range. You could step to a 225 tire and get the E load range but you have to have a 6 inch wide rim, minimum, which I bet you do not have.