Not by that much if the overall tire diameter is the same as stock. There are two ways that wheels affect braking:
The first is weight - big wheels tend to be heavier and the weight is closer to the outside, giving them a larger moment of inertia. A rough approximation is that a pound of wheel weight will have the same effect on acceleration and braking as 2 pounds of payload, so using fancy wheels that are each 25 lb heavier than stock is like picking up another 200 lb buddy on the way to the lake.
The second and potentially larger effect happens when you increase the overall diameter of the tires. The larger the diameter, the more torque that is required to produce the same acceleration or braking force. Torque is force X distance, so doubling the diameter would cut your braking force in half. More realistically, going from a LT245/75R16 to a 305/40R24 would increase the overall diameter by 3 inches (10%), which would have a similar effect on braking to increasing the weight of the vehicle (and the trailer if it doesn't have brakes) by 10%. If the combined weight is 8000 lb, you've effectively added another 800 lb as far as braking performance is concerned.
This situation can be avoided without reducing the bling factor too much by using 295/45R20, which are the same diameter as the stock 245/75R16 and have a sufficient load rating for a half ton. I still wouldn't want to be driving on any rough roads with them though.
and be safe.
