So, after I threw out the mono engine and gearbox sounds, I finally did some meters with the Euro 2 variants of the bus, and I have to say, that I had a lot fun! Despite that because I'm on the topic with my own Setra project, I have some things and bugs to mention. There is no order in my list, just as it came to my mind and my eyes 
1. All togehter together there are a lot differences between Euro 2 and facelifted version, that I miss in this addon. Let's start with the obvious one on the exterior. The air filter and the slots ot the air intake schould not be on the roof on Euro 2. It was moved up there with the introduce of the OM457 Euro 3 as this engine is bigger than OM447. So this sould be removed an as a result the scoops of the turbo fans mooved backwards. And btw. the openings of the turbo fans are completely missing in the interior.

2. there are some holes between intereior en exterior mesh:


3. I think on the upper handrail (on 315 Euro 2) should have some supports to the roof or the seat handles.

4. The emergency lever of the doors schold be different in Euro 2. And, btw. once open you can't close them anymore at the momen... (Sorry for using my own model but I just haven't a picture of an original at the moment)

5. You should check the templates. On 315 Euro 2 there is a position light not matching with it's shadow:

6. So let's move to the drivers place: As mentioned earlier by others, the gas pedal and the hand brake are different on Euro 2:

I also think the lever of the "bus stop brake" is too small.
7. There is a glass of an instrument left on the dashboard but the instrument itself is missing:

8. Small thing: As the auxiliary heating switch is without function it should be in "off" position, which is on all S31x always the on-postition of all other switches.
9. I miss a light on the dashboard indicating the active Retarder.
10. The door lights turn always on if you open the door. Perhaps it's a french specification but I only now it that you have turn on the lights that dhe door lights turn on when opening the doors.
11. People are stamping there Tickets without sound and stamper. You should remove the stamper entry in the passengercabin.
12. Speaking of the passengercabin: Some standing places seem to be a bit to low:

13. Speaking of to low: In my taste the bus is too low in the suspension. I corrected that for me changing the constant "bremse_level_setpoint" in the "bremse_constfile.txt" from -0.105 to -0.005.
On the other hand the ground shadow is way too high. it should only be about 2-3 mm above ground.
14. Last thing for now: Why didn't you use a envmap for reflections on exterior and windows as it is common in OMSI? So without the buses look a bit like "comic style". But this is a question of taste and easy to change by copy the envmap.bmp from anaother bus to the texture folder.
So that are my points, perhaps you can use some (or all?
of them to improve your product.