Quickest way is to go to your homescreen on sense, and try to pinch to zoom.
If you get the previews, your on 2.1, if nothing happens, 1.5.
Pretty simple right?
Oh and also you dont need to take it into verizon.
Are you ever going to root? Do you want to? If not, use the
ruu.
If you do want to root, check your hboot version (Which should be 1.47 since your on 1.5)
Turn the phone off, and then hold down the volume - button while powering back up. Youll see a s-off or on and then a hboot 1.47, 1.49 or something.
I completely advice rooting if its 1.47, but if its 1.49 for some odd reason go ahead with the ruu.
To run the ruu, just plug in the phone and run the .exe pretty simple and guides you through the process. It will wipe your phone though :/ But thats exactly what verizon would do if you took it in.