AFrame / Three.js : why so many (JS)Strings in memory, when loading complex .obj files?

we have a pretty complex webscene where we dynamically load pretty complex .obj- and .mtl-files. After comparing the scene without any of these objects with the one that has multiple objects inside we noticed a weird behaviour:

firefox memory heap shows that most of the memory (>500MB) is used for JSStrings. the rest of the memory is used for Objects which is self-explaining when we have complex object files in there.
But how come the high amount of Strings and are we able to reduce it?

We thought about minimizing the .obj files itself and reducing vertices. Maybe someone of you made similar experiences and / or can give us suggestions how to solve this problem.

Thank you in advance :-)