Unless we get some kind of bombshell that Martin has actually been writing both novels at the same time and they get released a year apart, there's no way A Dream of Spring will be released before the production and airing of the seventh season (or even a possible season eight).
There's always a way.
For instance, Martin could bring on a cowriter to do some of the heavy lifting on Dream of Spring
while he wraps up Winds of Winter
Or Martin could give up the Internet. Or the New York Jets. Or writing a script a year for the television series and having a role in the production.
It's a question of how he decides to allot his time.
And no, I don't think any of these ideas are likely.
By the way, Nate Silver's Five Thirty Eight
analyzes the stats and comes to a conclusion about when Winds of Winter will be released