On SYS modules I think it wouldn't make much of a difference although I don't have stats to back that up.
PREVIOUS has a very unique use case which is that you can refer the same line item in order to get the results. Now if you want to compare the performance between LOOKUP and PREVIOUS I think there were some stats shared by David Smith and I think PREVIOUS was doing better than LOOKUP. (I think)
@KirillKuznetsov That's a great question. I guess for the scenario which you are looking for, PREVIOUS would work better when you need to refer to a numbered value around Time as I guess PREVIOUS has been designed to work best for Time. These are my thoughts and would like to hear from other experts too.