I know BMI is not perfect, but using this as a ballpark ... at your height and weight yours is about 20.6I have 20mm of spacer so not really what most people would call slammed but yes pretty low I guess. And Long arms and a lot of hours playing snooker as a kid have given me the ability to get pretty long and low for 6’3.
Mine is currently 25.5 (still overweight)
If I got to your BMI I would need to be 9st 5lb or about 60kg S, I think having an end target of 65kg should be realistic (in theory). But you're right, take it as a slow burn, lb by lb, mostly done through diet/portion changes which is what I did for my first 10kg of loss. Not going to be easy though