Pictures of space?
Ripping out is unnecessary if it's just to insulate and the existing drywall is in good shape. As mentioned you can do blown in insulation into existing spaces like this by punching a hole in the top of the wall cavity with a hole saw to use as a fill hole for the blower hose. It's an easy but messy 2 person job and the blower is generally a free rental where you buy the insulation. Check my build thread in the sig, I did it on my current attached garage and still need to finish the job with installing the rest of the plywood "trim" around the top to cover the access holes.
For 15' tall walls, I'm assuming it's not framed with 2x4's so either metal, pole barn style construction or 2x6 framing(or larger) but either way you will need to do some "sleuthing" to make sure the cavity is clear of any "impediments" across the framing that would prevent you from filling it in a single shot from the top. Fire blocking or other items in that cavity would mean you'd have to put 2(or more) fill holes
"Pour In" foam is also an option, will be dramatically more expensive but should offer superior air sealing
Opinions vary on vapor barrier or no vapor barrier, but with it being un-insulated right now there is likely no vapor barrier between the studs and the drywall. If that bothers you there are paints specifically designed to be a vapor barrier that could be put on the existing drywall and remedy that concern. You'll likely need to get if from a "Industrial" paint dealer, the "retail focused" Sherwin Williams in my area don't have it but their professional/industrial targeted store had it in stock in 5 gal's:
https://www.sherwin-williams.com/painting-contractors/products/moisture-vapor-barrier
If you've got other moisture problems, removing drywall may be necessary to find and fix those issues. If there is moisture coming thru the walls post pictures of the exterior
Regardless of what you do with the walls, air movement is going to be important to have a comfortable space with that high of ceiling. Without air movement you'll get "stratification" in that space so your expensively conditioned air will likely be hanging out where you're not...no bueno! The "cadillac" of workshop/industrial grade fans is
Big *** Fans, remember though I did say "Cadillac" so have that in mind price wise. They're getting popular enough there are a number of other large diameter fans designed to move volumes of air slowly(which is what you want in a woodshop to minimize stirring back up dust) at lower price points
As to what to put on the interior, the "schools of thought" between what should cover the interior of a garage/workshop generally pit the camps of drywall, plywood/OSB and metal against each other. Each has it's benefits and each has it's detractors and what's right for one shop or scenario may not be right for another so read up and ask questions
When you get a moment if you'd also add your location to your profile it'll help get more targeted answers to questions like this as insulation or HVAC needs vary dramatically based on location.
