I only have a 30 day stamp on my entry into Thailand just recently. It's not a proper tourist visa (or is it?). If I go to immigration on the day before it expires do I get another 30days? I come from Australia. Or just 15? Confusion rules.

You can extend your 30 day visa exempt entry for 30 days at an immigration office for a fee of 1900 baht.

The 15 days is when doing an entry at a border crossing.

If I go to immigration on the day before it expires do I get another 30days?

Don't wait until the day before. You can go in during the week before it expires or at least a few days early. They add the 30 day extension onto your current permission to stay, so it doesn't matter if you go in sooner. You don't lose any days. If you wait until the "last minute" and get delayed in traffic or encounter some other unexpected delay, you'll risk sliding into overstay.

Edited February 22, 201511 yr by Suradit69