It would not be easy, normally would be done by a licensed tech.
The marks rarely seem to be on the same sheet but they are 215mm apart if you line the pages up in the order they printed.
I'm afraid my knowledge of the parts inside a Xerox 6015 is limited.
Would a transfer belt be easily replaced?
First try to measure the distance between two if on one paper that will give a clue to the circumferance of the part that causes the issue. Likely a transfer belt due to the size i see on your samples.
Second try to print a light coverage(30-40%) pure colors of C M Y and K and mixes too for yellow is hard to detect by itself. That will clue you into issues that plain text will not.
I am experiencing an issue with a Xerox 6015NI which keeps creating black marks on printed pages.
The black mark/smear is always in the same vertical position (see attached photos)
It seems to perfectly line up with the right hand CTD sensor but I have cleaned both sensors and the issue still exists.
I have also cleaned the LED lenses as per the manual but this did not fix the issue.
I'm hoping someone on here is able to provide some insight into what could be causing this?