Anecdata, but I had a Dell xps 15 with discrete nvidia graphics. Similar numbers to yours. For my next laptop I got a Thinkpad X390 and this little 13" laptop gets about 4-6 hours on linux, without any tweaking.
They claim up to 17.6 hours in tech specs. Did you check your workflow with Windows? 4-6 hours is nice, but if you could get full work day with Windows, it doesn't look that impressive.
