IQ of South East Asians:-

As suggested by Richard Lynn that South East Asians are fourth smartest group of people after East Asians, Europeans and Eskimos. Their PISA and TIMSS does not show the same.

Nations in South East Asia vs population:-

Brunei: 0.45 million
Cambodia: 15 million
East Timor: 1.2 million
Indonesia: 251 million
Laos: 6.557 million
Malaysia: 30 million
Myanmar: 51 million
Philippines: 101 million
Singapore: 5.5 million
Thailand: 65 million
Vietnam: 94 million

Total population: 623 million

PISA scores: http://isteve.blogspot.sg/2013/12/overall-pisa-rankings-include-america.html

White US: 518, SD: 100. (100 IQ)

Vietnam: 516, Thailand: 437, Malaysia: 413, Indonesia: 384.

TIMSS score:-
There is a table mentioned in http://raceandiqmyths.blogspot.sg/2016/10/iq-of-mid-eastern-and-north-africans.html

England: 496, SD: 100. (100 IQ)

Thailand: 467, Indonesia: 405, Philippines: 360, Malaysia: 514.

It is sufficient to focus on these 5 nations as these 5 nations make up 540 million out of 623 million population.

IQ of South East Asian nations:-
(*Note: I am using online normal distribution tool http://www.wolframalpha.com/widgets/view.jsp?id=67817f2e01eecd366e6d73ac7a71bcd1 to do calculations and can be cross verified)

Vietnam: 99 (PISA)
Thailand: 88 (PISA), 95 (TIMSS)
Malaysia: 84.5 (PISA), 103 (TIMSS)
Indonesia: 80 (PISA), 87 (TIMSS)
Philippines: 79 (TIMSS)

Most results on PISA and TIMSS across multiple edition are same.

Overall IQ (average for TIMSS and PISA):-
Vietnam: 99 IQ, 94 million
Thailand: 91.5 IQ, 65 million
Malaysia: 93.75 IQ, 30 million
Philippines: 79 IQ, 101 million
Indonesia: 83.5 IQ, 251 million

Overall IQ for SEA: 87 IQ

As per PISA and TIMSS, IQ in SEA is slightly (one or two points below) MENA region which has IQ of 88. And marginally above India which has IQ of 86. However unlike MENA which suffers from extreme fluoride contamination and India which suffers from extreme malnourishment, the reasons for lower IQ in SEA is unknown.

260 million popultion of SEA is Malays. In Singapore and Malaysia, Indian and Chinese minorities outscore Malays on IQ tests, education and economy by a decent margin.

So, based on my estimates and calculations; SEA is fifth smartest group after East Asians, Europeans, Mid East and South Asians. Eskimos are too small in numbers to be considered as a major group.