I do not know what the limitations of KiX is in that regards, while it may take time to search an array with 1.5 million entries, it is not like you are going to be doing this on every users workstation. It may be inconvienent for the person that ends up running the script.
Others may be able to answer if there is a limitation with KiX in regards to the size of the array's that you would be working with.
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