What is the average package of the IIT Ropar CSE? Is it a good choice at an AIR of 2145 in the JEE Advanced?

This year, the IIT Ropar CSE average package stood at INR 28.72 LPA which is pretty good for a new IIT. other statistics of the CSE branch have been tabulated below

However, judging an institute's worth on the basis of its placements is a wise thing to do. It's best to analyze your own preferences and also consider going through the course structure of the courses.

Coming to the second part of your question, yes, IIT Ropar CSE is a great option for those at the mentioned rank. The department has a highly learned faculty and provides a plethora of opportunities to its students. So go for it!