Call me cynical, but it could also be that AMZN will be automating all those lower paid jobs - as in: soon they won't even need 7.25$/H employees because they'll have machines. In this scenario, 15$/H would just be their current price point for the following tier of bottom of the chain not-yet-automated tasks.
This does produce temporary dislocation. Once all the elevators were automated, elevator operators were all out of a job. [1] But I don't think that's an argument against automation. I think it's an argument for a strong safety net and generous retraining programs.
[1] Yes, this was once a job. There are even a few left: https://www.nytimes.com/2017/12/16/insider/manual-elevators-...