Defined benefit pensions are generally seen as valuable, and hard to replace by investing on your own. So my default assumption would be to keep that pension, unless you think there's a significant risk the pension fund will become insolvent, in which case the earlier you can get out the better.
Obviously, you need to look at the numbers. What is a realistic return you could get by investing that 115K? To compare like with like, what "real" investment returns (after subtracting inflation) are needed for it to provide you with $10800 income/year after age 60?
Also, consider that the defined benefit insulates you from multiple kinds of risk:
- investment risk: your own investments may not perform well enough to provide the same benefit.
- inflation risk: this is sort of connected to investment risk, but worth thinking about carefully in itself. If inflation jumps up, would your investments also perform well enough to offset that?
- mortality risk: you live longer than average.
Remember that most of your assets are outside the pension and subject to all these risks already. Do you want to add to that risk by taking this money out of your pension?
One intermediate strategy to look at - again for the purposes of comparison - is to take the money now, invest it for 10 years without withdrawing anything, then buy an annuity at age 60. If you're single, Canadian annuity rates for age 60 appear to be between 4-5% without index linking - it may not even be possible to get an index-linked annuity. Even without the index-linking you'd need to grow the $115K to about $240K in 10 years, implying taking enough risks to get a return of 7.6% per year, and you wouldn't have index-linking so your income would gradually drop in real terms.