I had been shopping for the past few months before settling on a base 2019 CPO - you will probably find it difficult to get them down to $45k, but it doesn't hurt to ask since it's definitely within the pricing zone for a 2018 w/15k mi.
For example, this one with an MSRP of $67k with similar miles is at a 45k asking price:
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So that tracks with the $49k asking of the one you're interested in with the higher MSRP.
Going 10% below current asking price may be tough but not impossible if the dealer is motivated. FWIW I got 8% off the asking price on mine (~20% off MSRP for a 2019 'new' demo w/ 5k mi, CPO).
I emailed quite a few dealers and my experience with all of them was that they're very direct with a "no" if you go too low. If you ask them how much movement they have on the car and offer a little more, they'll usually counter with their "lowest I can go is x" figure - if this is substantially above 45k then you have your answer on how realistic it would be for them to go down to 45k and you either adjust your price point or keep shopping.