You've got a few options to clear the cache on the Droid Turbo 2 with using an app.
Motorola walks you through the process of clearing the cache partition on your phone using Android Recovery to this on
this page.
Verizon provides an alternate approach, either clearing the app cache for a single application, or the cache for all application -
instructions here.
These are all quick, easy and effective. You can also use an app to handle this - and there are numerous apps that address this in the Play Store, many of which are free. I hesitate to recommend a specific one, as I tend to personally be very cautious about these, and suggest that if you consider using one, make sure it has a high download count (in the thousands) and a high rating (e.g., above 4.5). There's a pretty good article covering the overall topic on
this page.