Do you have any lable indicating the GAWR? This is required to be on all RVs when sold new. I know of no reason for an owner to remove such a label.
If you cannot find the label have you tried contacting the RV manufacturer?
If you don't know the axle rating you have no way of knowing if you are overloading your RV or not. You should also get your RV weighed. Ideally you should know the individual tire loads. You can follow these
If you can't get individual tire loads then at least get the total for an axle and assume one side has 55% of the load.
With the actual loads known when the trailer is fully loaded with food, water, clothes etc you then need to select tires that EXCEED the highest measured load.
ALSO in the future you need to be clear when listing a tire size and provide the complete information such as P235/75R15 XL or ST205/70R14 LR-D
The letters in front of the numbers and the Load Range are important information.