Or -otherwise

Hello,

1. Shut the window, or it'll get too cold in here.

2. Shut the window, otherwise it'll get too cold in here.

3. Shut the window, or else it'll get too cold in here.

Is it always possible to replace 'or' with 'otherwise' is such conditional cases?

The sentences '1' and '3' are the compound ones.

What would we call the #2? (compound or complex or anything else)

Thanks.