Is it? It’s ok to get a second opinion from other dentists.
If their current position isn’t causing you pain or tooth/jaw wear problems, then straightening them is a cosmetic decision. And if you didn’t even realize they were that crooked until the dentist suggested straightening them, then the cosmetic aspect hasn’t been bothering you.
In my country (US), dentistry is notorious for upselling unnecessary cosmetic procedures.
For example, I went to a new dentist and he found two “developing” cavities he wanted to proactively drill out and fill and a “flaw in the enamel” he could fix with a veneer. I thought that was weird since I have never had a cavity before in my life and the “enamel flaw” was cosmetic only and never bothered me. I went to another dentist for a second opinion and she told me my teeth were fine. 5 years later and those “developing” cavities never formed.