I wish you would change your flight to Thailand...as you are going to arrive VOA Visa on Arrival and ONLY get a 15 day STAMP on arrival.
There is NO extension of stay at Thai Immigration offices when you arrive VOA Visa on Arrival.
Read this post and you may be able to do border bounce at select Thai land border crossings to get a New VOA Visa on Arrival stamp.
AND if you do receive the Thai Tourist Visa which you say is pending approval...
Then use it to get the 60 day stamp at the end of the 15 day VOA stamp
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