A leased tag group can use zero as its idle pace, which is interpreted as to not read at all.
However, you should read some prior discussions here on optimizing AB Logix. Start with this topic:
Read the whole thing. As you go through it, open tabs to referenced discussions and read those too. If you can, also open tabs for the back-linked discussions (the small links under comments).
It is easy to organize a Logix PLC to yield pathological communication loads from external users.