I'm curious if you don't use TImageList but instead TBitmap or something like that directly if it would be better.
Also instead of TPanel, try TCustomControl.
I have a motion graphics app with Cocoa and the speed was OK, but I use TBitmap + TCustomControl.
If changing to TBitmap+TcustomControl doesn't work, then this will be very challanging to fix. Cocoa drawing APIs are pretty crappy, so a lot of data copying operations are needed.