I will update my MacOS 10.15 Catalina two days back, after updating printer is not supporting
As you can see from our Compatibility Matrix Xerox will not be releasing Catalina drivers for the WC 6015. However, you can still add the printer on macOS using the built-in “Generic Postscript PPD”.
If Xerox driver features are really needed, you could try an unsupported work-around in which you install the Xerox macOS Common Print Driver from a closely related product which is supported on Catalina. Note that there may be incompatibilities that could cause not all feature/function to work properly
For the 7835, here is where you can download the Catalina driver.
Why are you using a 7835 driver on a 6015?