I have lichen planus & was told by endodontist to get to my rheumatologist sooner. have spondyloarthropathy. i was told theres a 15% chance of oral cancer. i saw all the white lines on inner checks and color on tongue and have pain. how serious?

While "lichen planus" oral lesions can cause cellular dysplasia ("abnormal growth") and there may be a 1-5% risk of oral cancer (not "15%"), biopsy can substantiate the diagnosis, but see an ENT specialist for an exam and treatment.

I assume that if you have been seeing a root canal specialist, an Endodontist, that you are talking about oral lichen planus. Would recommend that you see a specialist in Oral Medicine or Oral Pathology for appropriate diagnosis/treatment rather than a joint/pain specialist Rheumatologist. Your General Dentist or Dental Society can direct you.