RE 500 Bullets had offset forks and 19" wheels for years and everyone was happy.
The factory decision to fit 18" wheels front and back on the first C5 models was overturned in favor of going back to 19" fronts, so clearly 18" wasn't a good idea. When the Redditch (UK) factory fitted 17" wheels front and rear to the 350 Bullets for 1959 they fitted forks with almost no axle lead. Back to Chennai, and the Electra-EFI/G5 and the first B5 models had leading axle forks with 19" wheels and everyone seemed happy with those. I'm using early C5 and B5 forks on a pair of Redditch-framed bitsas, but with - you guessed - 19" wheels up front.
We've been spared your rain-grooved highways here in the UK (I've heard they can be a challenge even for a bike with good handling), but if your bike is otherwise fine a 19" front wheel swap, possibly with front fender and stays to match, might be all you need. Otherwise I'd be looking to test-ride the 2015 bike over those rain grooves, to be sure, which would also let you check out Wildbill's point on improved general build quality at the same time.
A.