How to improve performence of CRM_ORDER_MAINTAIN?

Hi Experts,

I am doing lead upload from flat file using CRM_ORDER_MAINTAIN.

If the file contains records upto 50 ,it is taking aorund 6 to 10 min.

If file contains records upto 100,it is taking 30 to 40 min.

For around 250 records ,it has taken around 4 hours.

Please advice on improving the performance.

Thanks,

Adi.