Most of my juices are 50/50 pg/vg. No idea what yours are however I have the same coil and usually run it between 10-11 watts. Your 8.5 wattage is a tad low and you might try cranking it up a bit if your mod will allow it. If it starts to taste burnt back off on your settings.
Again though, I doubt you will get any better result as far as your juices flavor longevity is concerned. Especially with such a large amount in the tank.
Try a little higher wattage and a lot less juice in the tank. like most, i'm very much in the habit of carrying around a small bottle of juice and a spare coil, J.I.C.
I typically get a minimum 2 weeks good use from my "genuine" aspire BVC coils. I don't chain vape though....