Have I made a huge mistake?!

[latearrival]

Hello.

I'm very new to this genre (about 10 hours with SH4!) and I wonder if anyone has an opinion or can help...

I just purchased SH4 (v1.3) from Steam, played for a few hours, and then went back to Steam and bought the U-Boat Missions, which seemed the easiest way to get to v1.5 (I wanted a read-out of my hull integrity, which didn't seem to exist on 1.3).

In my very limited experience, v1.3 seemed very stable, however v1.5 has been shocking. In the few hours hours that I've played v1.5, I've experienced:
- Crash to desktop;
- Being repeatedly told I'm passing the thermal layer when I'm cruising on the surface;
- Crew manning the conning tower when I'm submerged;
- Clouds on accelerated time, when the rest of the sim at 1x;

I'm running Windows 7 64bit. Have I made a huge mistake by getting the U-Boat Missions or is there a way I can get v1.5 working as it should?

Cheers!

(Until now I've been a flight-simmer, but sub-simming seems like it might be pretty cool!)