Is this a good rate of vocal improvment?

That is quite a quick improvement. An audio sample would be helpful. However, looking at the range you have, I suppose you have learnt to use your chest and pharyngeal resonance properly and now you are only having problem to cros the bridge from C, C#, D . Next step should be learning a proper mixed voice (chest + head resonance) and in the meantinme still working on limiting the strain from voice - which I mean - learning to relax your swallowing muscles and keeping the adam's apple at rest (in the middle of your throat).