use of subs var in rules

Summary:

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Hi

I have written a script as below

Where always the first variable takes value from best estimate scenario. and then other periods will take the prior value of prior period. and then additional 4 years are configured.

This takes some time to run. is there any other suggestion to improve the below script

"S1120022"
(
if(@ismbr(&RFPer1->&RFYr1))
"S1120022" = ("S1120015"->&LastPer12->&LastYr12->"Best Estimates"->"OFS_Load");
elseif(@ismbr(&RFPer2->&RFYr2))
"S1120022" = ("S1120015"->&RFPer1->&RFYr1);
elseif(@ismbr(&RFPer3->&RFYr3))
"S1120022" = ("S1120015"->&RFPer2->&RFYr2);