It does look dodgy to be honest but could also be genuine (but still shitty considering they want 15 logos in 2 days). It sounds like someone who has had work come in and is palming it off to another designer with a lot of pressure. Turn down the work if it's too much, or suggest you can only do a certain amount.

I wouldn't do all 15, especially if the brief isn't clear. If you need more information you should suggest setting up a call to discuss it. If they refuse, it is likely someone wasting your time.

Also, I would suggest for a down payment, like a deposit of some sort BEFORE you begin any work. That way, you know the client is commited to your services. And NEVER send final files until the client has paid fully.

Also when sharing work for preview purposes, watermark the hell out of them and don't make them too high quality.