From 1.5kg wet weight and now you done a bit more trimming i would of hazarded a guess of around 250g once fully dried and cured, perhaps a wee bit less. But 250g is half a pound (1kg = 2.2lb). Normally you could say wet bud will lose 75-80% of that weight whilst drying, and curing will result in minimal weight loss. I would be surprised if you ended up with under 200g although that still a good amount of bud from 3 months of growing an auto.
Did you cut off the water supply 2 days before chopping and leave it in the dark for that 2 day period?
Dry enough to grind after 3.5 days sounds about right but i would still leave it to dry a bit longer. You need a stem to snap and not bend before starting to cure. If you really want to go all out for curing get some glass mason jars and small hygrometers to go inside them. That will give you a constant measure of the RH inside the jars and glass is much better than plastic. Keep RH in the jars around 45% and you'll be sorted. If you see any moisture inside the jars while curing then take out the buds and dry a bit more (a few hours should do). If you dont then you could lose your crop to mould. You've mastered the art of growing, now you just need to master the art of drying and curing, not that there has been any problems in the past (especially from what i have sampled - and you do grow some good sh*t) but most people still learn something (even experienced growers).
When do you chop your other baby?