If I understand this right, you're making an initial payment of 15,000, the value of which grows by 5% in the following year, before you make another payment of 15,000.
You would then have paid (15,000 × 1.05) + 15,000 = 30,750.
The following year, you will have paid (30,750 × 1.05) + 15,000 = 42787.5.
In Excel, the best way to work this out after 25 years is to put 15000 in a cell (say A1), then in cell A2, write =(A1*1.05)+15000 and fill down to A25. Your final answer is in cell A25, which I make to be 715,906.48.
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Tue 11 Oct 2011, 22:37, 1 reply, 14 years ago)

I just did it by hand and got £751707.72
But I assumed that the 5% would be paid at the end of year 1, not year 2. You would expect investment growth in the first year, but I have simplified the £1000 a month plus tax relief to £15000 a year which will slightly skew the result.
(dozers, do fuck off ur a nob m8, Tue 11 Oct 2011, 22:52, Reply)

But then I used Excel and got 641764.50 in year 25.
Adjusted for the AMC at 1.5% until year ten, then 1% from 11-25.
(dozers, do fuck off ur a nob m8, Tue 11 Oct 2011, 23:06, Reply)