Does it make sense to study in a language school?

I’m moving to Japan for a year in June with a WHV, and I’m considering going to a language school of some kind to learn the language. I’ve been already in Japan for 3 months before (January - April 2026), and my girlfriend is also Japanese, so to also improve our conversations, I thought it’s be a wise idea to actually study the language there during my stay. However, I’ve heard horrific stories regarding Japanese language schools, specifically in regards to the stress it causes to students having to study 4-5 hours/day for 5 days + doing long homeworks, and the fact that language schools don’t really teach you how locals speaks, so I’m quite unsure whether it makes sense for me to spend money and efforts in a language school. I know how to read and write hiragana and katakana and I know quite a few words/sentences as my gf teached me them during my precious stay. My goal is to communicate, so I’d rather stick to learning vocabulary and grammar to build sentences, rather than learning how to read/write (especially kanjis). What makes most sense for me? What was your experience? Would doing a part-time job help me with learning?