In my experience LX is really the slowest of all major airlines. The OP's experience is quite normal for them.
While I agree to take some more time on day time flights, I usually have to do some work as well and would very much appreciate if they could limit the service to 2 hrs. On night time flights, it should be around 1 hr. Many airlines can achieve this with good service standards (AC, BA, KL, AB ...) or even with onboard chefs (TK, OS).