Investment strategies for those closer to retirement than to the start line?

Like the title implies, I'm in my early forties. Struck gold with a dream house and dream job, have some cash on the side but I'm unable to pull the trigger mentally for investing in equities. Reason for this is that my retirement window is 15 years from now and the possibility of a Nikkei scenario bothers me. It doesn't even have to be that bad, the SP500 had numerous "lost decades" itself. I'd really hate to go all in on now and end up being underwater at retirement. Anything I can do to mitigate this? If I was younger, I wouldn't mind, but the feeling of being closer to retirement really put things in perspective for me. Should I just go 100% bonds and aim for real-estate at this point?

edit: One thing that was suggested to me was using bond returns to purchase equities, does this sort of defensive approach make sense?