BDMV to mkv untouched 1080p

i want to convert my BDMV folder on my hdd to .mkv , with no dregade/change in quality

i tried handbrake , seemed quite friendly to use , but still left me with

a few concerns/questions

My original BDMV folder was just over 15 Gigs in size , when converting to .mkv

i was sure to check large file size ,as i presumed this would give me the highest

quality .

What i got was a file just over 1 gig in size . im not complaining or being rude ,

but thats one miracle in...

BDMV to mkv untouched 1080p