PVOH is in general troublesome to dissolve but it will do so eventually. Your grade is very highly hydrolyzed with a high viscosity and may be particularly stubborn. The major challenge is to avoid the early formation of a dense gummy clump of PVOH of granules stuck together. This will starve the polymer of water and you won't ever get it dissolved. You need to get the granules to swell as much as possible before they get stuck to one another. I've found success by initially using room temperature water and shaking sufficiently to prevent clumping as the granules swelled over at least the first hour. I recommend some kind of automated agitation, doesn't have to be vigorous you just need to prevent clumping. Initially it is all about diffusion. I don't bother heating it and going about fully dissolving until after leaving it overnight. Early heat can lead to early clumping.
You should test things out on a smaller scale until you have the process down. Then try and scale it up and solve whatever new problems arise. This is as much art as science at times. Good luck!