That's strange.. I don't know about cower.xml (since it seems to crash no matter what XML file I try it with), but MaXML 2 should be able to load a 15 MB file in less than 3 seconds (at least on my computer). Maybe you're forgetting to turn debug mode off?
You're probably forgetting in the differences in speed between your computer and others' computers.
However.. what the heck are you doing with a 15mb Xml file? If the data is that large you would probably want to consider using a binary format, or at least compile the Xml data to a binary format.