<< triangle mesh object

I have totally forgotten this apect of the problem! :)

So what is best : quadrangulate then decimate or decimate then quadrangulate ?

PS when i said 90% it's a big Decimation! (10% will be quasi no decimation)

Here the model OBJ
https://sketchfab.com/3d-models/graphosoma-lineatum-59fa16902b924d26bde9e626c76bb28d#download