If in case i apply for a single entry TR visa with a validity period of 90 days and I'll be granted a stay period of 60 days so if i would stay for 30 days in Thailand from the first day of the visa validity period and leave the country for 15 days, then apply for re-entry permit. Would i be granted 15 more days by the immigration or 45 more days as the total validity period of the visa is of 90 days?
TLDR : Answer Summary
When you enter Thailand with a single entry TR visa, you're granted a maximum stay of 60 days, and this stay period is all that matters when determining how much time you can spend in the country. If you leave Thailand before that 60-day period ends, the re-entry permit allows you to return without losing your original visa validity; however, it will not extend your total stay beyond the initial 60 days. If you're planning to stay for 30 days and then leave, consider entering visa-exempt instead to maximize your stay.