Just found a disadvantage of exporting and importing as obj. Although the amount of polygons stays the same, the object is twice as big. Imported as dae it was 330 kB and the same object after export and import is now 780 kB. So first I'll try changing all values of the weird dae import to zero. If I don't run into problems, I do not use export / import as obj. Probably I can dot that later at any time.