I hope this isn’t off topic …. I have an iPhone 12 Mini and I want to buy an iPhone 15. Should I go to the Apple Store or Verizon? I will not be trading in the 12 mini.
Should have them transfer my stuff? I don’t want problems with Verizon and transferring my phone number.
Assuming you already have a Verizon account, it shouldn’t matter whether you buy from Apple or VZW. I’d go to both sites and see if one has a better price than the other. Both are going to be selling it for MSRP, but there may be some deals available from one and not the other.
These deals are typically trade-in/upgrade deals, which won’t apply if you want to keep your old phone, but there may be others as well.
As for transferring your stuff, you can do it yourself. Verizon should include an instruction sheet with the new phone (if Apple doesn’t, you can download the instructions from Verizon’s web site). A quick summary is:
Back up your old phone. Use iCloud or a USB connection to a Mac or PC.
Disable “Find My” on the old phone
Power off the old phone
Power on the new phone. Set it up without restoring any data, in order to activate its pre-loaded eSIM for your phone number. Shortly after activation, your old phone’s SIM card will be deactivated - it will no longer have access to the cellular network, but should continue to have Internet access via Wi-Fi, if you need to use it again.
After confirming that the new phone is working on the cellular network (I recommend you place and receive a voice call and browse a web site or two), restore the (new) phone from the backup you made (of the old phone).
Once the restore completes, all your data will be on the new phone. For the apps, there will be placeholder icons. The actual apps will download over time from the App Store. Depending on how many apps you have and how fast your Internet connection is, this might take a few minutes or a few hours.
After the restore completes, you should also set up your Wi-Fi. If your backups were encrypted, then your login credentials should have restored with everything else. If not, provide whatever passwords you require as a part of connecting to your network.
Once you’re happy on the new phone and you no longer need the old one, you can wipe it via the Settings app. This will clean off everything so you can safely give/sell it to someone else.
If you really want Verizon to do this, they should be able to, but there might be a fee, since they probably expect you to do it yourself.
Me, my husband, and other friends and family members have gotten very good help setting up and transferring new Apple devices in Apple Stores. I’ve also heard good things from people who ordered stuff from Apple shipped to their home or office, and had Apple helpers talk them through the setup process via phone.
Even though you will be getting help transferring, it’s a good idea to check out this info:
Transferring from a 12 mini to a 15 in terms of just getting your data, apps, and settings migrated is trivial thanks to the great tools Apple built into iOS. The initial setup assistant (“Hello screen”) will take you through it all — it’s a piece of cake, no special expertise required. Having a good backup on a local Mac or on iCloud in place first is best practice.
IMHO the tricky part, or rather the part you can least influence yourself, is migrating from the old nano SIM to the new eSIM. That part involves the carrier. Initially, I was expecting this is where things could get hairy. But, to my great surprise and pleasure, that went without a hitch on our T-Mobile iPhones. It just worked. Not long after following the on-screen instructions on the old and new phones, I ended up with a new iPhone 15 with perfectly working eSIM and an old iPhone 12 mini with deactivated nano SIM.
I cannot judge if on Verizon you will see the same seamless eSIM transition. Judging by how many people have to go through this and how Apple and carriers will not like to absorb a lot of cost from a huge volume of additional support calls, I would, however, take my chances now that I’ve seen that this can work perfectly.
How about you get your iPhone from whoever makes you the best offer and gets it to you quickest, and then you just start by doing it yourself following the on-screen instructions? If you then run into issues, you can always call Apple or your carrier, and if that doesn’t lead to immediate remedy, you can still take it in to one of their stores. Keep in mind, as long as you have that backup (ideally to both a Mac and iCloud), you risk almost nothing, so you could try almost anything. Good luck! 
@Simon Thanks for the encouragement and advice. I have done all my migrating in the past. I don’t know what has me spooked this time!
iCloud is my only back up. I have a mid-2009 MacBook Pro, running High Sierra. When I first got the iPhone 12 Mini, I was able to back it up to the MBP. I was running El Capitan then. When I “updated” to High Sierra, I couldn’t back up that phone any more. It will be a couple weeks before I can get the 15, I’ll let you know how it goes.
I buy my iPhones unlocked direct from Apple so I won’t be locked in to one carrier if I need to change. However, everyone’s situation is different, particularly financial. As for transferring, I’ve always backed up the old phone to iTunes on my iMac, then did a restore to the new phone. I have NEVER trusted backing up online be it iClod or any other service. But, as always, YMMV.
Oh, I always keep my previous iPhone to use as an emergency spare. I had to use my 3GS this way when I lost my iPhone 5 and then use my iPhone 6 when my iPhone 10 battery swelled. Currently the 6 is the emergency spare and the 3GS has been converted into an “iPod 3GS”.
Just to be entirely clear, even the carrier-specific iPhone 15 models Apple sells in the US are unlocked. The only actual carrier lock on an iPhone applies to AT&T installments. Details posted here.