Always maximize all tax advantaged retirement accounts full stop for as long as possible.
There are ways to get your money out without paying taxes if your income is low in retirement (like less than 90k/year for a couple). Check out
http://www.madfientist.com/traditional-ira-vs-roth-ira/If you change nothing at all:
Throwing 6k/year into a taxable account should net you 108k with a 0% real return. More with compounding. If I'm conservative, you'll have 4k / year you can take out of that at a 4% SWR (you can probably go up to 5 or 6% because you're talking 15 years for that money and not the 30 years assumed with the 4% rule. So lets say you actually had a return and you end up with 150k in the taxable and you can do 6%, you're looking at 9k/year I think you could safely take out of that.
Then you can do any of the ideas in that madfientist post to cover the difference between that 9k and your expenses. Heck you can touch the "contributions" to your Roth account tax and penalty free and that will probably have almost as much in it as the taxable account. So you're at 18k/year without even getting complicated. What are your expenses like?