Sounds like you maybe taxying a little too fast as well as over controlling. Try controlling the taxying speed using power rather than brakes. Reduce the power setting to slow down, add it on to speed up and avoid riding the brakes on a relatively high power taxy setting.
Look further ahead when taxying and that will reduce any over controlling and keep the nose wheel off the centreline to avoid typical C152 nose wheel shimmy.
Regarding time to progress.The aspects that you do need to time consider are your exams as they have a direct affect on how you progress through your flying training and if not done in a timely manner can cause you to waste money as you sit stuck, literally burning money to stay current at the particular level you're at. I see many students today stuck in the circuit unable to progress as they have not undertaken and passed air law, for example. Exams need equal amount of focus as flying hours.