Is the difficulty assigned by kenkoooo to atcoder problems are in terms of codeforces?? I mean to say suppose a problem is assigned difficulty value of 1500 on kenkoooo then what will be its approximate difficulty in terms of codeforces difficulty system.

According to the kenkoooo docs, problem rating represents the same concept as the Codeforces problem rating, i.e. 50% of people with the rating can solve the problem.

Hence your question is equivalent to "What is the mapping between Codeforces and AtCoder user ratings. As far as I know, there is no official mapping, and no easy way to create one, but this question has been raised at least 5 times: 1, 2, 3, 4, and even some discussion of ratings from rng.