Question: Right now USB C ports are just arriving in laptops and I unfortunately dedicated to go with a cheaper laptop (pc) but with thunderbolt-2. 

The thing I don't like about thunderbolt 2 products is the premium price you pay for the Lacie external drives with thunderbolt2. I hope that in the future USB-C devices will come out that will be a bit cheaper as the PC world and mac are seemingly getting 1 standard thunderbolt3 and USB-C.

Long story short will the thunderbolt 2 connection be of ANY use to me in the future world of USB-C on my windows laptop in regards to my normal USB3.0 ports? If yes then what applications of USB-C will it work with? 

The only application I really care about is if I could connect an external HD sold with the new USB-C to my Thunderbolt2 via an adapter. 

I am thinking I will only get a benefit from thunderbolt 3 devices that are labeled as such to get an adapter to thunderbolt 2 ports for me to get a speed gain compared to USB3.0. 

In short the whole idea behind these questions is to have a fast connection between disks and laptop as I am working on big files in Photoshop and TB's of photo's and film ect. Even if USB 3.0 is "fast enough" I would still like to have the Thunderbolt 2 speeds rather then the USB 3.0 speeds.

If it is compatible will the theoretical and effective speed of a USB-C to Thunderbolt2 connection surpass the USB 3.0 max speed?

Answer: 
In specific. Thunderbolt can carry USB but USB cannot carry thunderbolt. 

In general, as long as your Mac has any Thunderbolt connector, it is highly likely you will be advantaged to connect over thunderbolt instead of using USB. For my money even Thunderbolt 1 is superior in many ways to the best USB 3 chipsets we have today. Now - the above statement is going to be obsolete soon since the newest Thunderbolt 3 chipsets and USB Alternate Mode Functionality mean that USB can be other protocols and TB3 looks to be an awesome step forward for simplifying the need for adapters that you would need on Thunderbolt 2 to get USB 3.0 connectivity today.

* [What Thunderbolt to USB 3.0 cables/adapters exist for OS X and Mac hardware?](https://apple.stackexchange.com/questions/136143/what-thunderbolt-to-usb-3-0-cables-adapters-exist-for-os-x-and-mac-hardware)
this entire question is backwards... the old connection CANNOT be adapted to by a new one. You can't get an adapter to use USB-C drives on USB or Thunderbolt. You MAY be able to use Thunderbolt 2 on USB-C. USB-C is a faster connection, so you won't be able to shove it into a smaller pipe.