Noticeable delay MIDI

The preset you are using could impact the delay.  There is some built-in delay with any pipe organ because tone production in a pipe requires some air to already be moving before the drop in air pressure makes an audible sound--this is particularly true of large bass pipes which need the negative pressure to oscillate several times across the entire length of the pipe before the air escaping the mouth at the bottom of the pipe makes any sound.  Presets that aren't from the player perspective have more delay as the simulation includes the sound-travel-time in a large space between the audience and the instrument.

Experiment with different presets and see if there's any improvement in the delay, as it could be more to do with the reverb engine and delay settings than the MIDI interface settings.

Also, Organteq's cpu load is significantly higher than PTQ and the way it distributes load between cores is also quite different (as far as I understand it), so knowing what computer hardware and OS you're using will also help diagnose if it's something built into OTQ's code (either a bug or something to emulate a real-life behavior of any organ) or if it's how your CPU and chipset are distributing processing that's slowing things down.  An e-piano will always have the fastest response time because it's using on-board, pre-recorded samples that are playing out of its internal speakers, OTQ has a much longer signal path of keyboard -> interface -> pci/usb bus -> cpu -> OTQ -> cpu (for real-time sound "invention" instead of simply RAM sample playback) -> sound card -> monitors/speakers with the cpu being, by far, the largest gating factor for speed.