Putting the summers back on, I was reminded again that the 15s I use for the summer change the steering feel rather dramatically. It's like a very positive camber, where the wheel pulls hard back to straight when you are holding a turn, speed independent. The 14s that I use for winter are very neutral, requiring very little effort to hold a turn. The 15s are only a 5mm difference in offset from the 14s. My initial thought it to get a new alignment done with the 15s on, but I don't want the 14s to be super squirrely when I put them back on later this year...

Thoughts?

I've always been told to do an alignment when you put new sized tires on. Maybe go to a shop and ask their opinion though.

Yea I generally get the car realigned every time I swap the tires. It's only $45 at Brakes Plus and only takes an hour or so. But it may not be that. Different wheel/tire combinations can feel very different. I know when I had my '90 Civic hatch and I went from the stock 13" steelies with 165/70 tires to 16" alloy wheels with 205/40 tires it was a HUGE difference in steering feel. Obviously that was a more drastic change than you're talking about, but just giving an example.

Well, any time you change wheel or tire size, it's going to feel different. Usually that's due to a difference in diameter, width or weight (especially weight). Depending on what kind of tires you had on the 14s, your 15s are probably heavier than your 14s, which puts more stress on the steering rack and all the front suspension components. However I think the mid-turn sensation you're experiencing is probably more likely due to front toe being off...I'd have a front alignment done, like others have said it's not too expensive and you'd only really need to have the front done.