Much depends how and when your redundancy pay is paid to you.
If you get the payment with your last month's salary, your taxable earnings to date will be £125,000 (£15,000 + £110,000). Assuming you will be on a tax code of £1060L (£10,600 personal allowance), the tax deduction on 30 June 2015 will be about £45,117.
In the 2015/16 tax year, you will have a gross taxable income of £146,000 (£15,000 + £21,000 + £110,000). The first £31,785 will be taxed at 20% (£6,357.00) and the balance of £114,215 will be taxed at 40% (£45,686.00). Your total tax liability will be £52,043 which is only £6,926 more than the tax deduction from your June salary and the taxable redundancy. You won't be entitled to a personal allowance as your income will be over £120,000. You get a proportion of your allowances and the 20% and the 40% tax band depending on how far into the tax year we are.
If the redundancy payment is paid to you post P45, a tax code of 0T M1 will be operated which will increase the tax deduction significantly. You should try to avoid that if possible.
As for your pension, you could try to have the pension payer take on the P45 figures so that the accumulated tax is adjusted in each month for the rest of the tax year so that at the end, you are all square as far as tax is concerned.
Alternatively, you could contact the tax office after the dust has settled and have them adjust the pension tax code by taking account of the tax that has been deducted from your redundancy pay so that by the end of the tax year, you are also all square as far as tax is concerned.
I hope this helps but let me know if you have any further questions.