My roommate has a BMW sportbike, because we're classy like that -- anyway yeah, you're gonna be leaning forwards more and yeah, the jacket's gonna ride up. Two schools of thought.... A, just by wearing any PPE at all, you're a step ahead of the crowd, and if this is only gonna be temporary you're probably going to save yourself a lot of money if you stick with your old gear. B, all it takes is one shitty driver to put you out on the dirt, and apparently you've got at least one in your neighborhood, so take protection seriously if you've got the cash and pick up a new jacket.
B is obviously safer; A is a little more logical. You decide where you're at on that spectrum -- it's probably a money question more than anything else. If you can afford new gear, hell, why NOT pick up a synthetic jacket? It'll look tight, and you'll never have a better excuse. If money's not THAT loose, then hey, ride it around in your current gear for a little bit and see if it really bothers you.
My gut says if you're hitting the pavement, your leather's gonna do just as well as anything else would. It's gonna come down to rider comfort, so.... you know, go see if it's comfortable.