The rating doesn't correlate to ride comfort like it did back in the day. I didn't believe it until these Baja Legend 17s (D-rated) rode more plush than my STT Pros (C-rated).
That's not to say that a different set of 17s won't ride worse or a different set of 15s won't ride better.
Wonder what the load rating is on your tires. I have Yokohama Geolander MT 33x12.50r15’s. Max PSI is 35 psi on the sidewall. I run them at 24 psi. I work at a tire shop and we use load calculators to determine proper tire pressure. We take the OE tire’s load and compare it to the new tires load, and adjust the PSI lower to make up for the increased carrying capacity. Makes for better traction, ride, and tread wear.
There’s your problem. Assuming your 33” tires are 10.50s or 12.50s you should be running NO MORE than 25 psi.
Every aspect of the ride, handling & stopping will improve as will the tread wear. Running those high pressures your treads will wear out in the center.