McP77

Wouldn't fancy it myself. That is one heavy tile. So you know that two walls are brick and two are plasterboard stud. Do you know that these walls haven't had a plaster skim. If any plaster then safe weight goes down to 20kg per square metre. I suspect that these travertine weigh around 30-35 kg per square metre on their own.

Preparation - rip everything off. Check tiles aren't too heavy for plasterboard. If so go for aqua panel.

Adhesive - white, flexible cement based adhesive.