Would this make my Macbook a powerhorse?

https://www.kickstarter.com/projects/ex ... the-ex-cor

I use a Mid 2015 Macbook, i7 16 gb ram, AMD Radeon R9 M370X 2048 MB

No....

My opinion is that laptops are not ideal for Resolve. Having said that, they were demonstrating some laptop editing with Resolve at NAB, so it can be done with light-duty proxies. Once you're finished, relink that session on a bigger system for finishing using the original camera Raw files, where you really need the GPU and CPU power.

The kickstarted project looks great, but I have my doubts on how useful it would be to you, especially due to your computer being too old, you need Thunderbolt3, which a 2015 MBP does not have. I would also not spend that amount of money with no guaranteed results with the software you intend to use it for.
If you want workhorse power from a laptop you have to pay for it. Check here for more insight... http://barefeats.com/rmbp_node_pro.html

I spend the better part of 2 years working on a 2013MBP Retina 15' with DR12
And, although absolutely not the best solution, if its all you have there are some options to make your grading/editing experiences more enjoyable.
The best bang for bucks and performance i found was to put a TB(2) connected small 4 SSD drive RAID ZERO array on my macbook. ( It also had a large mac TB cinema display on it and even mini montor to SDI grading display as TB2 is fast/wide enough)
That would act as a super fast cache / working media storage for all the media you edit with. I was even grading heavy multi layer EXR files out of Nuke, which is crazy I/O intensive and pushing it a bit (not fun but this way doable). For editing you create proxies in Prores422HQ or even 444 works fine (for grading) as Macs like Prores.
My workflow was always to transcode EVERY piece of media into Prores before i start with editing/grading.
If you then stick to normal grading nodes a refrain from too many ofx / noise reduction etc. You can have a pretty good experience.
If you do start playing with ofx/noise, do it at the end of your work and cache these nodes so during your main activities it is smooth sailing.

Its all doable by just beeing a bit smart in planning.

External GPU's could add to this equation but you need at least TB3 for these types of things. By that time better build a hackintosh with a proper GPU in there and you will be much happier for likely about the same amount of money.

thanks guys yea I actually dont have a problem editing my 4K RAW files after I make proxies (prores proxy and 1/8th quality) and it edits like a breeze. just wondered how much a difference this guy would make. My first step would probably be to get a RAID set up because I just edit on a regular LaCie hard drive standing alone. This graphics card would help with things like OFX more?

The GPU would help with some OFX, though not all OFX plugins are GPU-accelerated. It also can help with de-Bayering raw footage, and with some image processing.

Without Thunderbolt 3 it's not worth the bother. With Thunderbolt 3 it's still at best an interim solution.