The estimate printed by "kill... with statusonly" may indeed not be accurate. It is difficult to accurately predict how long a rollback will take, some of the reasons have been mentioned above.
As it happens, the accuracy of "kill... with statusonly" was improved in ASE 15.7 ESD4.2 (as well as 15.7 SP100), so hopefully that will give a better experience. There will always remain an uncertainty factor though, this cannot be avoided.
