Peggy: Regarding your question of "how long", when first diagnosed with leukoplakia it took several years before it went to cancer (and it was always called, in my case, leukoplakia-I first heard of PVL from you). If your experience is like mine, steady monitoring with any necessary remedial work will keep it under control. My leukoplakia was first diagnosed late in the last century, maybe 1998 and the first cancer was found in 2003.
Unlike you, I've never experienced any mouth pain (except after the 2015 operation, of course).