The bike I have purchased shows 15k km on the mileometer which seems very low for a 16 year old bike. The bike doesn't look its been around the clock once already. The green book doesn't appear to have any records of mileages. Is there any way to check mileage history on Thai motorbike?

Not really, as no official records like reg docs

wear and tear, on a newish bike tyre manufactor date to see if they have been replaced

If its a new book there should be a red stamp on the front.Look at the chain length indicators, if its close to the front with no scars on the swingarm from sliding it back and forth its more than likely a babied bike. Unless of course its a new chain and a repainted swingarm.

If the speedo needle bounces up and down that's a suspicious sign.

A lot of bikes in small towns will hardly ever see 40k kilos, but red dirt everywhere from the roads.

Speedo needle does bounce at low-moderate speeds, what could that be a sign of?

When its turned back by hand the shaft holding the internal gears are slightly bent/or the shaft holes are slightly hollowed out from lifting the gear because they have to jump the cogs backwards to turn it back.

It's a very tight fit, but not as tight after the cogs have been forcibly jumped backwards.

If it makes you feel better, I bought my 999S, 6 years old with 10,500 kms on it.