Well this is my second winter in the GTA with my leaf so I can give you some local advice. First off it's much better this year than it was last year. I drive 140km a day and stop for a charge in the winter. My wife has since stolen the leaf from me as she doesn't like getting in a cold car in the morning. She does 88km a day (Ancaster to Oakville) on one charge and doesn't turn off heat. She just keeps it under 100km on the highway and in the afternoon avoids the highway as it starts off quick (bad for range) then gets slow. She takes Dundas street and it's about the same time.
Last year the worst I ever had it was using 80% of my battery to go 73km, 85% highway at about 90-95km/hr (56-60mph) but that was on days that was as low as -30c (I think that's about where C and F are the same).
A couple tips I would give. Make sure your tire pressures are set cold. Most dealers set them hot, it's just easier since the tech picks up a car drives it around then brings it into the shop. Also a lot of places will set a default 32psi for all cars. This was done when I worked at a dealer. For both my leaf and my cousins leaf they were delivered with about 30psi cold. Easiest way to do this without an air pump is to pump them up at the gas station to 10-15 psi more than you want. Wait till the morning then release air until they are where you want them.
If you've already bought winter tires and they aren't LRR then that's a big hit to range.
Since you have an SL you have the 17s, they are heavy, very heavy. I would seriously recommend getting winter tires for safety but you can also get a nice range boost by dropping down to a light weight 15 or 16 in rim and tire. My 15s are 30lb a corner, 16s can easily be 36 lbs and stock 17s are 49 I think.
For tires I would go with a Nokian Hakkapellita R, Kal tire or MTC tire Oakville (better prices at MTC). They are some of the lowest rolling resistance tires you can buy. Also go with a 205/65/15 (I run those) or 205/60/16 (my cousin runs that on his SL) as it's a bit taller for less rolling resistance. You can also go with a Michelin Xice as it's very good for rolling resistance (I have them on both of my Prii). You can also run both of them up to 51psi.
As for 15 vs 16. 15s are a tight fit, very tight. I would only go 15 if you buy something listed on tire rack. They offer it as an option on the 2013 Leaf SV so select that. Since the 2015 leaf SL you have has 17s they don't offer 15s. You can call them to double check fitment even if you don't end up buying from them.
The only light 15 they offer is the Motegi SP10 at 14.4lbs.
For 16s they have the Enkei RPF1, 13.7lbs but $211US each. I called a few years ago and the Kosei K4R at 12.4 lbs fit but since the centre cap won't fit the leaf they aren't listed. They are $159US each and also a high offset so they will pull in closer to the car and be a bit better for aero (to see them search under a Hyundai veloster).
For 16s there's also the Motegi MR125 at 15.4, Advanti B1 Lupo at 15.6 and the Fast Hayaku at 15.6.
With maybe the exception of the Kosei you should be able to get the Motegi, Fast and Enkei at any place around here. JRP in Mississauga is the distributer for Enkei in Canada so they'll have the best price. I know MTC Oakville carries fast, and you can find a ton of places on Kijiji selling them too as they are a Canadian company.
Hope that helps.
