Prediction of the IAT cutoff of IISER colleges is quite difficult. This is because they just tell you whether you are in or not.

However, the cutoff for the general category is close to 70 so you have a good chance of getting in the IISERs with 75 marks.

You should wait until the last round of counseling. For more information about IAT and other related queries you can go for the below link:

https://engineering.careers360.com/articles/iiser-merit-list-and-cutoff 

Best of luck!