I hate to ask...

[Straight6DOHC]

as it's probably been asked many times before (albeit worded differently)
Why would a 2018, 56000 miler at £52000 get a Porsche warranty/used/approved while a
15k miler for sale at, say, £46000 with better kit, wouldn't?

[Ed.Neumann]

A bit more context needed?


Maybe the 15k one has missed services? Maybe it has aftermarket mods on it? Maybe just aftermarket parts fitted?


Only way to know is ask, everything else is just guesses.

[NDA]

Are they both being sold through official Porsche centres?

Private sellers can transfer a warranty, independent dealers cannot. Official Porsche dealers can (and usually do) offer an official warranty.