I wasn't aware they don't come in 27.5, I can't imagine why... I did see a 26 at their site, (
https://www.vittoria.com/us/en/tires/gravel-cross/terreno-dry) so maybe one of the 700 sizes will fit a 27.5 rim- wheel and tire sizes are weird these days... Graphene is one of those catchwords that get associated with everything. It's hard to prove it works, or helps, or even if it's really in them. I can see marketers saying "well they've got carbon, and graphene is made of carbon, so, it's kind of in there?" Sooner or later, science will make advances and graphene may live up to the hype.