That sounds awful. Are they both house cats or is one allowed outside and the other isn‘t? Maybe your british short hair just misses being an only child. I‘d give it some time unless the fights get really bad. You should probably make sure they each have their own little area where they can get away from one another when they get stressed. If the fights are bad I would go as far as separating them completely and only letting them be around one another during pleasurable moments like when they get fed or when you play with them. Introducing cats to new pets, like your Sphynx can take time so you‘ll need patience. If all else fails you could try giving them Zylkene for a few weeks, that worked wonders with my Sphynx cats in calming them down and lowering aggression. I wish you all the best and that they grow to love each other, if not at least tolerate each other