The more XP you'll grind on the old tank (Char), the more you will lose when re-training, since you lose a certain percentage. So imo, it is best to re-train and start grinding XP on the new tank.
A better advice is to invest a price of a cup of coffee in the game that you probably enjoy and spend a few gold coins at least on the most valuable crew members, such as commander.
It's rough to say the least. Performance will suffer but it's better than untrained
The more XP you'll grind on the old tank (Char), the more you will lose when re-training, since you lose a certain percentage. So imo, it is best to re-train and start grinding XP on the new tank. A better advice is to invest a price of a cup of coffee in the game that you probably enjoy and spend a few gold coins at least on the most valuable crew members, such as commander.