InfoAssist can take a few minutes to open if the dataset being accessed is excessively large.
 

Select "Sample data" instead of "Live data preview" following the instructions below:

1.) Go to admin console from "management center" in WF-Client.
2.) In Configuration Tab, select "InfoAssist properties" 
3.) In "Tool option dialogue box", from "Data preview method", select Sample .
4.) Save and clear the cache.
5.) Now if you will open any new InfoAssist reports, this setting will be there.

NOTE: For the already existing reports, turn on the setting manually by doing the following:

1.) Open the existing IA reported created earlier, and select " Use Sample Data" from Home Tab.
(as shown below)

** Working with sample data makes the editing and processing faster especially working with million of records. After selecting the sample data , the data looks like as shown in attached "sampleDATA.png".

** As soon as you run the report, you will see the actual data.