Dataset schedule refresh time very slow.

Hi Everyone,
I have a dataset in service which uses a dataflow as its datasource. Dataflow refresh takes about a minute but what concerning here is my dataset is taking about 40-43 mins in every refresh. Table in dataset has around 60-70 million records. Also I am using Premium license.
Also dataset contains no other transformation or anything.
Any suggestions to optimize and decrease in refresh time will be appreciated.

Thanks in advance.