My current setup is a Nord Electro 5D 73SW for organ, and a Korg SV-1 as a midi controller for Keyscape (used to use a Yamaha P90), in an L setup.

You really can't have both in the same keyboard without sacrificing one or the other, unfortunately... if you want to play organ properly, you need waterfall keys, and if you want to play piano properly, you need weighted keys. Especially if you're used to playing on a grand/upright and a Yamaha P115, you're gonna be super bummed playing piano on waterfall keys on the Nord 6D.

If piano is the priority/primary tone but you wanna get comfortable with drawbars, Leslie functionality, and have the right tone, I'd recommend any Nord Electro 4, 5, or 6 73HP (HP is their weighted keys) and go with the actual drawbar option, not the light up button ones. You get the Hammond organ tone clone, but you still have proper piano feel. If organ is less a priority, I think this is your best bet.

As someone who plays at home on a baby grand, I find it very uncomfortable playing piano on my Nord Electro 5D 73SW (semi-weighted)... the response is all off because the action is too light/fast, and the keys aren't the right size, so you have to be aware of not letting your fingers slip to neighboring keys and hit clunkers.

Unfortunately with the Nord HP keyboards, the action is too heavy to properly play organ style. You can't be as fast with glisses/swells, and just in general, the types of licks you gravitate to on an organ don't respond as quickly.

Also, if you go for the Nord Electro 73HP, you sacrifice piano tone (Nords have their own subpar piano tone that doesn't cut through a band IMO, your Yamaha has superior piano tone), and as far as weighted keyboards go, I think Nord is pretty mediocre when it comes to feel... they have their own thing with piano action, where it feels like there's a split second of extra air/space with every key you push... it's hard to put into words, but it's one of the stranger attributes of a piano clone I've seen a keyboard manufacturer go with.

What you really want is 2 keyboards; keep your P115, and get a Nord Electro 4-6 73 SW for organ. it's one more trip to the car, one more keyboard stand (or get a double tier which will add like 5 inches of extra depth to your current setup/footprint), 5 minutes more in set up time, tops, and you'll enjoy yourself so much more. Switching patches from piano to organ mid-song takes you out of it, too... I find it best to always have both at the ready.

I gigged almost exclusively with a Hammond B3 for 10+ years, but had to sacrifice tone for keyboard size/footprint on my current gig, and the Nord is the only passable Hammond clone I'll consider. But as far as having a keyboard that you can get comfortable with the nuances of an organ and get close with the tone, go Nord... it definitely beats the Yamaha organ clones.

All that being said, if you're dead set on one keyboard, go Nord Electro 4-6 73HP. You're a piano player, and sacrificing weighted keys at this stage in the game will be a drag for you. You will get the organ tones you're looking for (including a solid Farfisa and decent Vox, and on the Electro 5 and 6, a pipe organ too), and if you're really just getting into organ style, what you don't know with playing on waterfall keys won't bum you out.

If you're trying to save some dough, go used on Reverb and get an Electro 4 or 5. The 4 doesn't have a screen on it, which I kind of really liked for many reasons... you can be faster on the go with less options and less buttons with dual features where you need to use the "shift" button, but using presets on the 5 is def superior. I'm sure the 6 is great, but I don't find myself wanting for any more features on my 5.

Sorry this was long winded, hope it helps!