Thanks for the replies. I do have the 19s and was expecting under 300wh per mile. Yes makes sense that 85kwh is high a number to use in calculations. In fact was wondering about it, so is it the case the usable power was May be lower than 85kwh even when new but does that go down as the battery ages?
Will watch for next few days and will get an average and compare it with what the car reports. Today the car reported 300wh per mile as average for the last 30 miles.
You need to remember a couple things.
The report Wh/mi number that's averaged over the past 30 miles is only while the car is being driven. Same for the Wh/mi number that is being reported in the Trips tab for the Trip A, Trip B values.
Any energy consumed while the car is parked and not being driven is not considered in either of those calculations, but directly comes from the main battery. This includes any energy that gets consumed by preconditioning, using cabin overheat protection, etc. Depending upon you use case, that can be very minor, or it can be very significant.
That's where trying to do any form of calculation looking at the total number of RM use, or percent battery consumed over time is only really valid if you're doing a continuous drive and not a variety of short trips and aggregrating them.
I have a mid-2016 MS90D with 19" rims. My understanding is the range and overall efficiency on the refreshed front end that I have is potentially a little better than your 2015 MS90D. From tracking data over the past 6 years on my car, I need to average around 274 Wh/mi while driving to achieve 1:1 between the indicate rated miles consumed and the actual miles traveled. That's where for your car you need to be somethere in the mid-to-upper 280's to reach that 1:1 parity point.
Honestly, the best way I've found to judge change in battery capacity over time is to simply charge the car to a set percent, say 80% or 90%, and then just track the displayed range in rated miles at the end of charging. You can ratio that to 100% and use this versus the stated range number for a relative change over time. That's an indication of the change in the available or usable energy capacity of the pack, not an indication that the efficiency (or Wh/mi) changes.