Not too bad on the speed really
On the basis it appears to have been an economy run with the best economy winning those speeds are allright, 20kmh below the wet weather and 40kmh below the dry weather motorway limits, and thats ignoring the fact it is averages which can be considerably lower than your top speed.
19mph seems poor in the mountains but then what Per Gunner Eriksson can do in a Ford Focus knowing there is nothing comming the other way round the corner and some bloke telling him exactly how sharp the corner is, whether or not there is a big rock sticking out and if the handbrake or scandinavian flick is a good option.
In comparasson it's range on a single charge is better than I can get out of 40L of Premium Unleaded (95RON), 30mpg if I stick to 50 up the A9, regular route takes 2 hours not caring about economy (22mpg) to do 94 miles, 47mph average speed. (A90 from dundee to Perth, A9 to Dalwhinnie, A889 to Laggan Bridge, then a small bit of A86, fair whack on HQ Dual carriageway, and usually get a fairly clear run on the A9)
I think it would be a great test of the Tesla, compare it to a 25 year old SAAB on a typical trip to the highlands.