AFAIK it's USB2. I don't think microUSB supports USB3 connection. USB 3 adaptors are different. See the Note 3 adaptor.
Also, after the Note 3, it was seen that using the old USB3 adaptor on a phone does more harm than good. USB-C is a different beast altogether that can support USB3 though.
The GS7 is USB 2, like it was said it is microUSB.
I believe some phones with Type C are usb 2.0 as well, for example the Oneplus 2 and Oneplus 3 are USB 2.0 but use the Type C connector.