When you rotoscope, it´s almost as if you think like an animator, just backwards. The key is to find as less keyframes as possible maintaining the natural flow of motion. With modern techniques like planar tracking and a bit of brainwork in order to keep things neat and break down complex movements into smaller and more easy to handle shapes, things can be sped up quite a lot without loosing too much quality.
I wrote an artivle about how to tackle rotoscoping here, but unfortunately it´s only in german.
some exaples of rotoscoping i did: