Construction costs are currently skyrocketing

Two empty conduits, I think DN40, each with a 3x1.5 cable. I have now also read afterwards that this is only supposed to be sufficient up to 15kWp, according to the general contractor. But I am already skeptical about that.

What do you want to do with the 3x1.5? I would say 4-6² DC cables go in there. Two pieces per planned string. Additionally, preferably in a separate conduit, a fairly thick and stubborn grounding. Then provide two network cables and two 5x2 (or thicker, depending on distance) for two wallboxes at the parking spaces. Because if you have photovoltaics first, the e-car will definitely come afterwards. And vice versa.

now you already have SHOULD, see above :)

It's gotten pretty off-topic now.

What does it look like specifically for those who are currently requesting quotes? Is the extreme trend continuing overall like that?

What do you want to do with the 3x1.5? I would say, 4-6² DC cables go in there. Two pieces per planned string. Additionally, preferably in a separate conduit, a rather thick and stiff grounding. ...

Our neighbor is installing 3 x 10mm2 for his system. But his is also a bit larger.

Our neighbor lays 3 x 10mm2 for his system. But it is also somewhat larger.

that depends on the wiring:

the respective extreme configurations are:

- all panels in parallel: then the maximum possible current flows,
a rule of thumb is max 10A/m² conductor cross-section

- all panels in series (only 1 string):
here the current is minimal and the voltage max

both rarely occur in pure form.

Common is the parallel connection of several strings (series connection), each requiring one cable to the junction box.

The configuration depends on what the subsequent on-grid inverter can/cannot handle or requires.

16 panels can thus be wired as 2 8-string 2p8s or 4 4-string 4p4s
(even 8 2-string 8p2s would be possible)

Reverse protection diodes should definitely be clamped on the panels.
Otherwise the entire output of a string fails if only one solar cell
(e.g. shaded by stuck-on leaves) is shaded.