I was wondering if having 2 wifi dongles attached to a Raspberry Pi 2 will be faster than just 1 wifi dongle connected. They will be both connected to the internet. Surely it should have an increase of some speed?
On their own with nothing else, no they will not work in tandem. You would need to configure your networking to manually split traffic by application or use bonding as described below to have the kernel do it for you.
This is called
Ethernet Bonding in linux , and is supported by the kernel (and thus all major linux operating systems). Generically the term is also known as
You are not guaranteed any increase in throughput or speed, this depends on context (transfer size, destination, network conditions, other network equipment etc.).