OTR uses DH in a ratcheting protocol that requires attackers to continuously break new DH exchanges; it's not like TLS, where one exchange at the beginning of the session gives you the whole session.
Also, while a 1536 bit modulus isn't the best you can do in 2014 (we should all be using curves now instead of doing DLP crypto), it's probably not within reach of attackers right now. Effort doesn't scale linearly from those 1024 bit factoring problems.
Also, while a 1536 bit modulus isn't the best you can do in 2014 (we should all be using curves now instead of doing DLP crypto), it's probably not within reach of attackers right now. Effort doesn't scale linearly from those 1024 bit factoring problems.