Thank you for bringing this to our attention, we can verify that there is indeed a performance hit in this case.
Going into 2022.2 we modified the audibility system internally so that it would work with send/receive on mixers. This modification gets quite expensive when the underlying audio graph is large (as is the case with this issue). We have plans internally to re-work the audibility system so that it is more performant, but it is sadly not a quick fix as this part of the audio system is complex - so any changes come with a high amount of risk.
If at all possible we recommend trying to lower the audio source count (2500 is pushing the audio system very far!) as well as lowering the voice limits from their maximum.