Rob
Ansys Employee

2d has it's own problems as the wake separation may be asymmetrical and 2d-axisymmetric will mask that. Inflation shouldn't add too much to the cell count, and some careful decomposition should mean you can tet only the near sphere region and hex the rest. 

Also, check sphere projected area and then read up on wind tunnel blockage factors. The domain looks fairly big relative to the sphere so you may be able to save some cells that way. 

Finally, Student is intended to help you learn how to use the software. That includes realising you need a bigger mesh to get the right answer, and is why we also have Research licences.