Well, I think you are "jumping the gun" here. Your load capacity, that in addition to the trailer, is over 2,000 pounds. I don't see how you could come anywhere near overloading that trailer. IMO, you have plenty of load capacity with the tires you have. Secondly, there is only 2" of space between the tires on our Surveyor 235. I bet your measurement is similar. Realize that any larger tire will have a larger diameter. So, they probably wouldn't fit; the tires would be in contact with each other. D rated 14" tires are hard to find. Kumho makes a D rated tire in 14" that is speed rated to 99 mph and yes it is a trailer tire. But the aspect ratio is different; 82 vs 75 so you would need to do the 195 size to get the same diameter as your current tire. You would gain load capacity. We have the same size tire as you have on our 235. We've towed 10's of thousands of miles on them; all day in extreme heat, over horribly rocky national forest service campgrounds; all without incident. IMO, you are fine and should just make sure of your load, speed, trailer balance, tire pressure. Remember trailer tires are only rated for 65 mph.
2012 F150 FX4 Ecoboost, 2016 Surveyor 274BHS
2003 Yamaha FJR1300, Demco Premiere Slider
1969 John Deere 1020, 1940 Ford 9N, 1948 Ford 8N
Jonsered 535, Can of WD-40, Duct Tape
Red Green coffee mugs