Yes, there is a minimum of personal income required to apply for LTR Visa depending on the category you will apply to.
Wealthy Global Citizens: minimum personal income of USD 80,000 per year in the past 2 years.
Wealthy Pensioners: minimum personal income of USD 80,000 per year.
Work-From-Thailand Professionals: minimum personal income of USD 80,000 per year in the past 2 years.
Highly-Skilled Professionals: minimum personal income of USD 80,000 per year in the past 2 years except for professionals working for Thai government agencies.