XML DSIG schema validation performance

Hi,

I have a XML DSIG enveloping document I need to validate against its schema.

I´m using Apache Xerces 2.6.2 for schema validation (full schema 
validation). Everything works fine but process takes about 10 seconds. 
Using the same class with other XML documents (even using very complex 
schemas like UBL standards), validation never takes more than 2 or 3 
seconds (start JVM, locate class, create parser, open file, etc.).

Has anyone any experience validating this type of documents? I´d really 
appreciate any advice or idea.

Thanks in advance
Jorge Ortiz