As I said previously, you are crossing the end of the tax year so you cannot compare your pay for March 2015 with that for April 2015. They are two different tax years.
If you earned £173,750 in 2014/15 (£170,000 / 12 x 11 + £215,000 / 12 x 1) you should have paid tax of £64,315 for the year. Check your 2014/15 P60.
If you are now on £215,000 you should be paying £6,908 per month in tax.
The figures above assume that you have no employment benefits such as a company car or private medical insurance.
Unless you complete annual tax returns, you can have your 2014/15 tax checked by contacting the tax office on the number here
and asking them to issue a P800 tax calculation for the 2014/15 tax year. You will need to tell them if you had any other income in 2014/15 such as savings interest, dividends, rental income etc.
I hope this helps but let me know if you have any further questions.