Call of Duty: Vanguard

As the description says, you need to get a kill with 15 different weapons throughout the campaign, across all missions. While this may seem like a lot at first glance, you'll be playing as four different characters in four different parts of the world, and since each country has its own guns, you'll unavoidably make plenty of progress (and almost assuredly outright complete) this achievement by the time you finish the campaign. Almost every mission starts you with a unique weapon specific to that character, so you will unavoidably get 5-10 kills even if you somehow never switch weapons in the campaign. If you finish the campaign and still haven't unlocked this achievement (the achievement tracks, so you can see how close you are), the first mission in the game, Project Phoenix, actually contains over 10 different weapons:
 

• STEN (starting weapon) 
• Top Break (starting sidearm) 
• Machine pistol
• STG44
• Type 11
• SVT-40
• PPSH
• MG42
• KAR98K
• Volksturmgewehr
• Einhorn Revolving

​​​​​​Beyond that, as noted, you'll get some unique weapons for each character, such as the Requiem with Polina, Owen's Gun with Wade, the Bren with Lucas, etc. So as long as you switch it up every so often, especially when you're running low on ammo, this achievement will come naturally before you even finish the campaign, without really trying.