by even training with a 1.5 hours intensive training you do also some "aerobic exercise" ,and this will be also sufficient...

the main thing why thais do not get tired lies under the fact i.e. they know also how to breath, how to slow down and speed up correctly ...in the west people mostly attack to the hell and making pressure ,if they find the opportunity and forget mostly correct breathing...contraversary,as far as i see the thais know much better when to breath...teeps (push kick) are playing a big role in this concern...when they "teep" they also breath deeply...and also i have seen that some fighters are making breathing exercises during or at the end of training...
by the way, the high number of their fights also presenting them orgaanize how to berath and make the best optimization of energy systems...they are getting big experience due to frequent,high number of fights...