London - England desperate to justify CWC favourites tag
But since then they have climbed to the top of the ODI rankings, mainly as a result of putting their trust in a fearless brand of cricket for which Buttler is the standard-bearer.
"The biggest learning from that World Cup was sort of how far we were behind the best teams in the world at the time," he told reporters at England's tournament kit launch on Tuesday.
"We had to change quickly and adapt to the way cricket was being played and start afresh," added Buttler, also England's ODI wicket-keeper.
That change in attitude was evident in England's first ODI after the 2015 World Cup.
They beat New Zealand, that year's losing finalists, by a mammoth 210 runs at Edgbaston after posting a total of 408 for nine featuring Buttler's whirlwind 129 off 77 balls.
"That series we played against New Zealand straight after the World Cup was brilliant for us," recalled Buttler. "That first match we were 200-odd for six at one point but we still had the guys to take it on.
"We were at rock bottom and that meant we could play without many limitations," he explained.
And yet it is an innings of 110 not out off 122 balls - Buttler's slowest ODI hundred - which saw England to a tense one-wicket win over world champions Australia at Old Trafford last year that he rates as one of his best.
"I think being not out at the end is a great feeling," he said. "Walking off knowing you hit the winning runs, even if it's just 10 or 15, it's great to be there at the end, especially batting in the middle and trying to see the team over the line."
England World Cup squad:
Eoin Morgan (captain), Moeen Ali, Jofra Archer, Jonny Bairstow, Jos Buttler, Tom Curran, Liam Dawson, Liam Plunkett, Adil Rashid, Joe Root, Jason Roy, Ben Stokes, James Vince, Chris Woakes, Mark Wood