Xmlport takes long time to create Sales Order(NAV13 r2)

I have created xmlport to create Sales Oder. It takes approx 2 minute to upload 1000 excel lines , but when upload 10000 lines then it takes 2minutes to upload 10%(1000 lines) …20% takes 30 min…and to upload 100%(10000 line) takes 6-7 hours. I didn’t find main cause of delay.