Comment by qesa

Using the file from the original,

    1#desc sum each group (!/) (" II";"\t") 0: `:tsvfile

Took about 3 seconds, 2.5 of which was reading the file

EDIT:

    q)\ts d: (!/) (" II";"\t") 0: `:tsvfile
    2489 134218576
    q)\ts 1#desc sum each group d
    486 253055104