What “C” means in this context
On common van/commercial sizes, a C marking identifies a commercial-vehicle tyre specification. These tyres are intended for the load and service demands of vans and light commercial vehicles.
What XL means
XL means Extra Load within a passenger-type tyre standard. It increases load capability compared with a standard-load passenger tyre of that type, but it does not automatically make the tyre equivalent to a commercial C tyre.
Why the physical size is not enough
Two tyres may both say 225/75R15, but construction, load index and service description can differ. Choosing only from width/profile/rim diameter can put the wrong tyre on a working van.
What to send when asking Thunder
Send the full tyre marking, including the C if present, plus the vehicle and how it is used. For commercial work, load requirements matter more than simply finding a tyre that fits the rim.