Dave

I wouldnt leave it down as it could debond in the future even if it seems well glued now doesnt say in time it wont....remove the vinyl and any glue residue ( heat gun will help with this )...prime with bal apd neat and tile using bal rapid flex white and grout with bal wide joint grout with bal GT1 admix.....seal the tiles before and after grouting.. use a 6mm solid bed trowel ........dave..