My flatmate does history of art with museum studies and although she has less lectures than me she has more than enough work to make up for it outside of uni! Not to scare you, the workload is comparable with any other degree really, and as long as you do it when it's set you'll be fine. Just don't leave things like essays til the last minute, otherwise you'll be really bogged down. Don't worry, I'm sure you'll cope fine!