I also am not totally into 15's on the car but I put function first over form and the 15's I have look more like 16's due to the design so I am OK with it. I did pick 17's for the street setup as was able to find a good combination.
I have autocrossed on and off since the early 70s's but seldom do so now, every few years maybe, too much standing around, not enough time behind the wheel. I have lived in 4 states, different ends and the middle of one so have been in many regions and always enjoyed the autocross crowd, they are especially great here in Utah. I am going to take my car to a couple events to shake it down a bit before going to the track but more to see the people I know at them I have not seen in some time, many great people, some good friends now.
I understand your method of moving up in tire width and grip, makes sense, I do it more with power than anything else, I guess all the years of setting cars up, which I am better at than driving them it seems, helps me go fairly fast right away and seldom have anything go wrong with them. I have always been very competitive in class but I learned a valuable lesson one winter while building a Vette race car, a really nuts car at that. I organized and ran an indoor kart series, even if I picked the fastest kart I ended up in the back of the pack as the local racers, instructors, champions, etc....were just better than me. I then realized I was putting all I had into a car far beyond what I should be driving and was going to have to put a driver in it, young guy at the kart track was the Red Bull shootout champion and faster than anybody but did not get a ride as the economy was in the pits. Ok, putting $125k in parts, into a race car I could not drive, operational costs were huge, I was doing all the work......did not make much sense so I parted it out and sold nearly all of it off. I have the chassis and suspension and a race LS engine still that I bought a 53' Studebaker body to make a pro tour out of, street and track of course. It is for sale, I have built it in my mind a few different ways and just do not want to do the dirty work, lots of it.
Anyway, back on topic, I understand having fun in a little FWD as I have had my most fun in them, autocross and track and dirt roads and.....for some reason I just fit with them and faster than in anything else like RWD and AWD, finding the right wheel and tire combo to fit ones needs, skills, comfort zone, very very important.
Rick