If you have made posts in the lounge then they don't add to your post count and why wait until 15 posts to talk about music? Surely you can talk about music seriously if that's what you are here for.
If you are here just to promote a band then the posts will be deleted anyhow so the 15 post rule discourages trolling as the posts are deleted and accounts banned if it's promotion and we can tell in just a few posts if people are spamming just to promote something.
Happy posting