If you look at this table you can see the big differences:
Faction | Shells | Vet 0 Cooldown | Real Vet 0 cooldown | Vet 2 cooldown | Real Vet 2 cooldown |
Soviet | 8 | 78s after last shot | 78s | 60s | 60s |
German | 12 | 83s after first shot | 22s | 62s | 0s |
That's why I propose to change the cooldown on the german howitzer to start after the last shot has been fired. This would mean the cooldown would be more in line with the Soviet howitzer and be 83 seconds for Vet 0 and 62 for Vet 2
If you look at the overall balance it would make more sense, the German faction has more offmap strikes and many more commanders with recon plane to deal with emplacements and static defenses.
For the rest I think the Howitzer are balanced well, the Soviet is better against vehicles and first strikes while the German has better fire rate and superior area denial.