You can watch ASL videos and compare them to LIS. They will be different but that doesn't mean you can't learn both. Even though they are different, learning one sign language gives you the basic tools of thinking conceptually and expressing yourself visually. Those abilities will carry over into other sign languages.
You're already bilingual in spoken language, so you could just as well be bilingual in sign language.
If you're looking towards interpreting as a career, the more languages you are fluent in, the better. It opens up more opportunities.
