I’ve played both side by side and own a ES920. Also plays a P-515 regularly at work.
ES920 has a warmer thicker main piano sound than P-515. It’s very nice to use. Unfortunately as with all digital piano you can hear that it is digital. When I first listen to it I get the feeling that there is something wrong with the eq-setting. The eq-sliders at the piano doesn’t help with that. But you get used to how it sounds, just like with an acoustic piano that is slightly out of tune.
P-515 have a thinner but very precise main sound. The eq-“problem” isn’t as big as the ES920 but the P-515 aren’t trying to mimic such a warm sound as the ES920 with its CFX-sample. The Bösendorfer is almost unusable in my opinion, it lacks dynamics and clarity.
I like the action on both. IMO the Kawai is more slippery, the Yamaha has a nice texture that gives extra control. The P-515 has a harder felt where the keys hit the bottom that I believe makes the fingers a little bit more tired after playing for a while. Seems to be typically Yamaha. I like the softer felt on the ES920. The P-515 is faster/easier when it comes to repetition of a key.
Since this is a keyboard forum I must comment the USB-possibilities with the pianos. P-515 has USB-audio and MIDI witch makes it excellent for hooking up to a computer, iPad or phone as an external sound source. The ES920 on the other hand has only USB-MIDI and on my piano there is some strange USB power leak that makes my MacBook lose its ground. You can feel it when you touch it and when you send the sound from the MacBook back to the ES920 via a 3,5 mm cable there is a hissing sound. This is a problem that makes me thinking of changing my ES920 for a P-515.
The ES920 have easier access to overdrive/amps for electric pianos and the overdrive sounds better IMO. On the P-515 you have to press a lot of buttons for adjusting overdrive.
The weight difference is notable but shouldn’t be the only selling point.
