Mitchell: England women face tougher autumn than Rugby World Cup
The Red Roses face France and New Zealand at Kingsholm and Twickenham respectively next month before travelling to Canada for the top tier of the WXV women's tournament.
They take on the hosts and the United States before clashing again with New Zealand's Black Ferns, the reigning world champions.
In four of their next five matches, Mitchell's squad play three of their major rivals for the 2025 World Cup in England, with France first up for the Red Roses on September 7.
"This is probably the most important pre-season leading into the long-term goal," Mitchell told reporters at Twickenham on Wednesday.
"And the short term is probably harder than a World Cup with the two warm-up Tests before we go to WXV."
Mitchell, a former head coach of the New Zealand's men's national side, added: "It's a great challenge. Logistically and rugby-wise it will be just as challenging, if not more challenging, than winning a World Cup.
"To win a World Cup you've got to win the last three games but we've got New Zealand twice, France once and Canada once. They're the top three teams in the world."
Mitchell led the Red Roses to a dominant defence of their Women's Six Nations title earlier this year, the team completing a Grand Slam and scoring 270 points at an average of 54 per game.
But by 2025 it will be 11 years since England last won the Women's Rugby World Cup.
The Red Roses have lost the past two finals to New Zealand, including an agonising 34-31 defeat in the Covid-delayed 2022 edition.
"Our game's definitely working but we want to get faster at it so we're looking to add to our attack and our defence," said Mitchell.
"We've got what we call DNA strengths that we could always go to, but I see a happier playing group when they're all involved in the process of attack and in the process of defence, not just relying on units.
"The capacity of the girls is definitely growing and we're building resilience, which is going to be needed over the course of the next 400 days with the home World Cup coming up."
