Reorder lines near the beginning of a huge text file (>20G)

I am a vim user and can use some basic awk or bash commands. Now I have a text (vcf) file with size more than 20G. What I wanted is to move the line #69 to below line#66:

$less huge.vcf
...
    66 ##contig=<ID=9,length=124595110>                                                                                                                                                       
    67 ##contig=<ID=X,length=171031299>                                                                                                                                                       
    68 ##contig=<ID=Y,length=91744698>                                                                                                                                                        
    69 ##contig=<ID=MT,length=16299>
...

What I wanted is:

...
    66 ##contig=<ID=9,length=124595110>     
    67 ##contig=<ID=MT,length=16299>                                                                                                                                                  
    68 ##contig=<ID=X,length=171031299>                                                                                                                                                       
    69 ##contig=<ID=Y,length=91744698>                                                                                                                                                        
...

I tried to open and edit it using vim (LargeFile plugin installed), but still not working very well.