multi user picker listener add delays

[J C]

I am getting a 5-10 second delay when adding multiple users to a multi user picker using a listener in scriptrunner, is there a more efficient way to handle this:

List<ApplicationUser> newIAC = [];
newIAC.add(ComponentAccessor.getUserManager().getUserByKey(iacVal));
newIAC.add(ComponentAccessor.getUserManager().getUserByKey(iac2Val));

When I have separate lists that I add a single user to in the same listener, it works fine but only slows down when I add a 2nd user to any of the lists.

Thanks in advance!