TT-30P is 120V and the RV adapter you listed will likely put both hots on the same pole so nothing will happen. You will need an EV style adapter which I believe will switch the car to L1 so will likely draw 15A or 20A so 1.5kW or 2kW (some manufactures let you draw 24A on 120v, not sure about Leaf), but if you can use the full power of the plug it will be ~2.9kW.

My suggestion is reuse the 10 gauge wire and turn it into a 240V NEMA 14-30 (there is a NEMA 6-30 which is a better fit but I don't think it is common enough to find adapters) with some slim breakers and you don't need the neutral for L2 charging (keep the ground though). This means you should only pull 24A (80%) and if the EVSE or car can't limit the amps then you will need to get an EVSE that can. This will get you 5.7kW with maybe ~$150 worth of stuff (assuming you don't need to buy a 24A EVSE or lower) and ~1 hour of work. Look up how to charge a leaf on a dryer plug.

Alternative cheaper and will work is a TT-30 to MEMA 5-20, though will be L1 and slow like you stated.