It seems your mzML files are unsually heavy. Although this may not be a huge issue when dealing with only a few samples, with your study size the question of data conversion arises.
Before discussing an appropriate user quota increase, I would advise to first try to disminish your file size by reviewing your conversion parameters, since compression options may be possible without impacting the extracted information you will get using the XCMS Galaxy modules.
When using the MSconvert tool to convert raw data into a standard format (mzML here), there are conversion options that allow specific compressions.
You can find information about these options in the MSConvert documentation. What I advise is to check whether one of these options would be appropriate in your context and try using it to obtain lighter mzML files.
In case you are not very confortable with compression, do not hesitate to perform some tests on 3-4 files, trying extracting them in Galaxy.