If your final objective is to actually learn the essence of the language, go for it! JLPT, reading outside of school work or anything similar it doesn't matter.
I should stress on the fact that if you really wanna do well in competitive LOTE subjects (Japanese, Chinese for example), getting ahead of your peers and everyone else in the cohort in terms of content is definitely crucial. Not to mention the added benefits of constantly enriching your vocab and expression in a language!
Now I'm not so sure about Japanese (read the study design they seem to skim through fairly basic N5+tad bit of N4 level vocab) but for my Indonesian oral exam they actually drifted off and went beyond what was taught in the study design, so bear in mind that it might happen as well.
If you don't mind, what textbooks are you using? Would defs recommend Tobira: Gateway to Advanced Japanese if you're up for the challenge.
べんきょうがんばってね!