There is nothing to your question. You have answered your own question.
Immigration stamp you out the country on the 15th and you fly the 16th.
Do you think you need a visa after you have entered airside? Your in no mans land which means your neither in nor out of a country. This is the same all over the world.
Its very dangerous at the moment. I'd look at visiting Afghanistan and letting the Taliban know your scared of Thailand and ask if you can join them for a 6 month training camp to grow a pair.