To make it a little complicated, there are a few varieties of C3 Jay fins that I have come across on the market. I wont comment on how the difference in rake/shape between a C3 and a Deb will make the board perform, because its something I dont totally understand, however one thing I do know on the C3 Jays is that its important to have a fin that is torsionally stiff, to get it to work upwind (and downwind). By 'torsional stiffness' I mean if you put the fin in your board and turn the board upside down, then twist the fin tip left and right with your thumb and index finger (like you are unscrewing a beer bottle top), that is the torsional stiffness, as opposed to the stiffness we normally are talking about when you bend a fin over your knee.
The early Jay fins from Boogie werent very torsionally stiff, and as a result we found the Debs a lot faster upwind/downwind. A few of the boys down in Sydney worked with Boogie and managed to build soft fins that were torsionally stiff which were starting to get on par with the Debs. With the Sydney boys helping, Boogies fins were getting better and better and better with each new Jay proto, but unfortunately, Boogie now no longer makes fins. So there are only about 3-4 versions of these torsionally stiff Jays I have seen in existence which are all down in Sydney so my guess would be yours is an older version (>12 months old?), which would be soft, torsionally. This wont give you the same power as a soft Deb fin. ALL the Deb fins are quite torsionally stiff, whether they are S-- or H+, which is why they are such nice fins
So back to the point (lol), I think your Jay will be better (more power) than an R13 Hard +2 simply because it is softer and getting more power from the flex/twist of the fin than a H fin will, but it wouldnt be anywhere as good as a modern R13/R19 S- especially if you got one raked forward >+6cm. As a rule of thumb, I think the further you rake a fin forward, the more torsional stiffness you need to go downwind fast, because if your fin is twisting too much downwind, you are losing the loading you are generating on the fin with your legs as the fin keeps releasing (as it twists from side to side), which could also mean you spinout a little downwind or that the board 'fin-steers' (ie, the board controls where you go, instead of YOU controlling where you go!)
The R19 works great in the 159. In fact, it works fine in the 159, 160 and 161 (although with the 161 you can obtain the best speed/angles out of that fin). On the 159 with the R19 I use the mast track ALL the way back (ie, mast plate covering the serial number) with a 10.7 in all winds (a little further forward with 11.6/12.5 or if you are >90kgs in weight) and with the 161 the mast track a little behind centre (ie, 2cm behind centre) in all winds. With the mast track further forward you are pushing the nose of the board down which may give you an uneven loading on the fin. Also try filing the front (or back) of your fin head so you can adjust the rake 1-2cm while on the beach, and try your fin at a few different angles next time you go sailing. For every cm you change the rake of a fin you are changing how the fin twists/performs and this is very personal to your sailing style and maybe why you are getting spinout (strange, because I have never experienced spinout with the R19 in any board). There could be a host of reasons for spinout too (not enough downhaul, boom to high [overloading the fin], footstraps too far apart [incorrect loading of fin] ??? but probably you guys are good sailors and might know that already. . .
Testing gear is like computer programming, just try everything one step at a time and you will eventually eliminate all variables until you figure out why your spinning out.
Err...sorry about the long post :S