When will there be a new version of varia radar 515?

looking at 
https://fccid.io/frequency-explorer.php?lower=24000&upper=25000

Field Disturbance Sensor : https://fccid.io/IPH-04099 related to ertl-615 or something else?

You're right.  But it also could be the new radar is made to be wider than the existing one, one that contains a larger battery for a longer runtime.  I could also hope.

And a reflector instead of the plain black surface, meaning that you could comply with UK law at night without needing a separate reflector. 

there are more documents due by 2023-06-30 so we will know more in 2 weeks.

Nope, eRTL-615 is https://fcc.report/FCC-ID/IPH-04540/ (FCC ID is on the back side https://www.garmin.com/en-US/p/874099).

This is probably just a radar, without BLE/ANT+ as there is no lab report for 2.4GHz frequency. Just check label, there is 14/28 Vdc which is used on airplanes, it is related to GMN-01410 which is some flight thing and probably its new name is GHA 15 - there is no similar GHA product, so no clue what it exactly is.

In Switzerland, many online retailers are out of stock right now....could it be that a new version is going to be released soon? 

Even Garmin's own webshop for Switzerland states a delivery time of 5-8 weeks (!) (compared to the model with camera which has only a few days of delivery time)....Supply chain issues or new model coming up soon...that's the question.

competition heating up too with ANT+ Radar units from iGPSPORT and Cycplus at Eurobike 2023. along with Magene and Bryton