I have just started doing LII topic tests from CFAI website and they’re brutally hard for me. In many cases I recognize that I would need some basic conceptual knowledge I just don’t possess. I think LI material is necessary, unless you are an accountant (I’m not unfortunately).
There is not too much you need to know from Level 1 for Level 2 exam. CFA Institute will test in CFA Level 2 Exam based on CFA Level 2 curriculum Readings only.
OK than let’s say that if you have time to carefully read each letter of the curriculum, all answers will be there I’m 100% sure.
But because I study from Schweser (I do BBs and EOC from curriculum only) I often find that I should know something based on my LI studies (but I just can’t recall it exactly because I took LI in 2014.)