I understand that the Falken Ziex ZE310 is a good choice. For the size 185/55/15 there are only extra load tires, while for the size 205/50/15 it is "normal" tires.
I wonder if it matters if there are extra load tires on the front wheels? Can it be positive from the point of view of road handling?
I checked this as I was worried I might have missed that when I bought new Falken ZE310 Ecoruns for my TF. You are right in saying that in the sizes you want, which I believe are the correct sizes for 15" wheels on a MGF VVC, one size is V XL and the other is V only. On my 16" TF wheels, both sizes are V XL so the issue does not arise.
These tyres are very popular on both the MGF and MG TF, so somebody else must have encountered this. You could also try emailing Falken. Or you could contact Demon Tweeks for advice. They seem to do the best deal on these tyres.