I can offer a lot of ideas on the subject. First of all, let me explain.
Users often don't sign up here to do spam. They come to get the content they like. When they see the 15 message rules that limit them, they get annoyed and write absurd comments. And they get what they want. My suggestion is that after they become a member, they will receive an 8-hour counter. And let the countdown to make the forum appear. I think it connects everyone (new members) here. People value. You will be managing the most important time. This will give them a very good lesson. Nobody wants to spam after waiting for 8 hours. You should consider this proposal.