CPUs are soldered in these—Intel and AMD. Since the PGA option has fallen out of favor, most laptops made after 2013 are soldered.

In addition, processors like the mobile Xeon are reserved for high-end, multi-thousand-dollar mobile workstations like the Zbook, Precision, and P series, not entry-level models like the 15-p. The processors need a PCH that is Xeon compatible and tend to be as thick and heavy as many laptops from when they were crazy enough to put a Pentium 4 in a laptop. Yes, they are that thick and heavy due to having much greater TDP ratings than any HQ Core i series or Ryzen laptop.
Yes, the performance of a Zbook with an Xeon/AMD FirePro (ISV-certified Radeon) is MUCH more capable, but you’re going to pay for it, new or used. I’d LOVE to take home a ZBook 15 or 17 with the 4K 95% sRGB/DCI-P3 display for the price of an EliteBook, but most of them need a lot of work or have unknown BIOS passwords that may or may not be crackable at the time of purchase.