I think you can expect to see a similar pattern emerge (where fish of the minimum size limit are harder to find)-regardless of where the MNR sets the minimum size limit-- especially in lakes that get heavy fishing pressure.
It is pretty common for walleye to have boom and bust cycles where it appears that one or more year-classes are scarce in a particular lake. This phenomenon is generally thought to be caused by environmental conditions affecting the success rate of the spawn and subsequent survival of the fry. It seems to occur regardless of whether there are highly restrictive limits on minimum or maximum size allowed for harvest. That said, I have definitely noticed that catching 17-18" fish can be a bit more challenging in the northwestern Ontario lakes that I fish, but I've never noticed any problem with finding fish in the 15-16" range. Some of the lakes that I fish also have a "slot" limit that bans harvest of any fish in the 18-24" range and for those lakes I have noticed that we catch more fish that are 18-20"-- which I think is good as these are fish that should be left to ensure future breeding.
I think an important consideration is what you are hoping to "get" when you go walleye fishing. Do you want to catch a trophy (whatever that means to you) and be able to take it home to mount on the wall? Do you want to catch a few fish to fry up for dinner? Do you want to have lots of catch-and-release action? Do you want to catch a large stringer of fish and get a picture that shows what a great angler you are? In my opinion, the Ontario walleye regs are a good blend in that they allow you to possess 2 (conservation license) or 4 (full license) and that should generally be enough to feed the angler and a couple of friends as well as bring home a trophy if that is what you are looking to do (although I would highly recommend releasing that trophy and getting a replica made if you really want to hang something on your wall) while at the same time the regs do a good job of protecting the breeding population from over-harvest by anglers.