It depends on what file type you import. If it’s an .SKP (SketchUp) file format, we don’t have a file-size limitation, but heavy / large files can definitely affect the performance on the iPad (memory consumption wise).
As for other files formats such as IGES/STEP, it’s a little bit different. Bigger IGES/STEP files means lots of curves and control point and that means many mathematical calculations that would affect the performance of uMake on the iPad.
I would suggest slimming down the files before importing them, for example: removing unnecessary geometry and use only what you need when you travel. I understand it’s not ideal, but might be a good workaround for now.
With that said, would you be able to send us to “[email protected]” an example of a file you want to import into uMake? This will help us determining what’s possible to improve when dealing with files like yours.