An iPhone 6S from Germany will include all of the frequencies and types of service that a 6S bought at Verizon has. This includes CDMA, GSM, HSDPA, and LTE. Modern smartphones from Apple and Samsung will work anywhere and all Verizon smartphones are unlocked.
I have used my Verizon S6 Edge this summer with a 3 SIM in Ireland and a German SIM in Germany.
There is something odd about Apple smartphones activating in countries other than the one they are purchased in. My daughter is trying to activate her new German 6S on Verizon. Verizon said that the model she had would work, gave her a SIM and told her that the Apple servers were slow. The problem is that her husbands identical 6S will work for a few minutes after a re-boot and then it reads "no service." This has happened multiple times after re-boots.