执行时间较慢批量.xlsx到.xls转换

I have written this code to batch convert a bunch of .xlsx workbooks to .xls (I have a lot of end users using 2003). It does the job but it is very slow, I tested this on 20 workbooks each only about 30 kb in size and it took 9.78 seconds to execute locally. Through my sharepoint server this took 262 seconds but I believe the incredibly slow speed for sharepoint is a different issue.I have written this code to batch convert a bun