Is walking really a reliable way to lose calories?

I read that a 150 lb person who walks 10,000 steps a day loses around 500 calories, give or take.

At ky job, I can walk up to 15,000 steps a day if I wanted to. I'm young and have always been athletic (though that slumped in the last year and I gained 15 lbs) so after all the cycling and basketball I've done, it seems far fetched that walking would actually burn that many calories.

Any experience or opinions? Id like to just use my job and an aggressive calorie reduction to lose weight if possible. I'm 213 lbs, 6 feet