How to Speedup Formula processing

I have been using this formula which macthes the List of Cells to Raw String and if match found then write same value.

This function is working fine but it stucks and sheet gets stop due to the large set of data.

I would appreciate your help if someone can share a fastest way.

Sheet is stuck from past 10 minutes.

=INDEX($K:$K,AGGREGATE(15,7,ROW($K$3:$K450000$)/(ISNUMBER(SEARCH(" "&$K$3:$K$450000&" "," "&A3&" "))),1)