Q. Can a pillion rider sit sideways on this bike - R15 V3?

I took my mom for a short spin and she was sitting sideways. She can keep only one leg on footrest and the other leg was hanging .if the rider is more than 5.8 and the pillion rider is short sitting sideways then it's ok . Otherwise it will look awkward

Yes, but i wouldnt suggest you to sit sideways, because its going to be uncomfortable, & it will look very awkard.

Yes