Performance creating collection is slow

Performance creating collection is slow

Performance is VERY slow.
This simple code adds 20 seconds to the load time of a form.
If I move this code block to a "On User Input" the form loads instantly. When invoke the code it takes approx. 20 seconds to run.
Removing the sort does not increase speed of execution.
Removing the criteria does not increase speed of execution.
Repacing ui.add with simple string concatenation does not increase speed of execution.

for each rec in Deals [DealStatus == "Active"] sort by Deal_Name
{
DealsList:ui.add(rec.Deal_Name);
}

Please advise.
tt
tonythomas