Here's the fix for the problem you have encountered. I too have a OWC SSD in my early 2015 macbook pro retina and encountered the same problem as you and thought there was no fix. But don't be discouraged. . there is a fix and it works beautifully.
You must install a SSD firmware update in order to install High Sierra or Mojave on yr OWC SSD. Once the firmware has been installed successfully mojave will install without any problems. I typing this msg on my macbook pro with mojave so believe me it works. If you haven't done it you'll need to reinstall your previous os which might be Sierra. That's what I did before I did the following.
First, go to this link at OWC: https://eshop.macsales.com/Service/Knowledgebase/Article/26/730/Aura-SSDs-Firmwa re-Update-beta
Then, scroll down and download the two files that are listed, the firmware utility and firmware update. Open the utility first and install it, it will create an app found in yr applications folder. Once installed, make sure you are online for the app to work. Once online go in yr applications folder and open the 'marvel utility' and a window will appear, just like the image given on the webpage. From here just follow the instructions as given. The user name is the name you entered when you created your account on your mac . . . I guess for most of us it's our name. Then enter the password you use to log into your mac. Once this is done and remember you need to be online, just follow the instructions as given and . . whamo . . . your ssd firmware will be updated. Close the app and restart yr mac and follow the instructions to ensure the update was successful by confirming the updated firmware version number.
Voila !!! You can now upgrade your beautiful mac to High Sierra or Mojave. I've got mojave installed now and the installation process went smoothly. I think it's neat.
Let me know how it goes . . . this should no doubt work for anyone who has a OWC SSD in their mac.
I await the good new from you.