15 Years is surely not too late but it puts you into a pretty disadvantage.
- You cannot let time work for you through compounding
- You cannot let time work four you to work out bad times
These two constraints mandate an investment portfolio that is tilted towards safer assets and high contributions compare to a portfolio of your younger self that targets the same investment goals. However, portfolio allocation is one of the later steps in investment. The earlier steps are much more important and they can be performed at any age (and probably should be reviewed on a regular basis even by younger investors).
Quantify your investment goals
You are talking about retirement in 15 years but what does this exactly mean? How much money would you get from state pension, company plans, etc. and how much money will you need? How do you picture retirement? Do you plan to spend most of your day in front of a TV (like my grandfather) or do you plan to be active and travel the world? There is a huge difference between those two variants
Evaluate your financial situation
Make a list of all your income, your fixed spending, your assets and liabilities. How much money do you have left every month? How expensive is your mortgage and if it is expensive are there any prepayments possible? Are any repairs coming up on your house? What about your car?
What is your plan with the house? Do you want to live in it during retirement in which case its value would mainly be not paying rent (as realizing any price appreciation would require selling the house) or do you intend to move somewhere else and sell it (which would actually make it an investment)?
Piece the two sides together
Only once you know what you want and what you have to invest, you can properly decide how to invest. Go into yourself and try to determine how much risk you can take. Double-check this with your financial situation. Inform yourself about the investments available and do not trust any so called "advisors" working on commission.