It is more complex than just a physical reassessment. They are not only doing a reassessment of 20% of the properties but also a "
Statistical Update of values".
Here is a link to the town's explanation.
UPDATE.
Durham NH went through a Statistical Update of values in 2018
Durham UPDATE and their property assessments went up 16% as well. A statistical assessment assesses the whole town valuation and raises the overall assessment of town property valuation to match predicted current value. It is law that NH towns must make good efforts to keep assessed values as close to market as possible so they MUST do this. AGAIN, if the whole town is valued more and the budget does not increase, the tax rate will drop and your tax payment would not change.
Further, it is not clear to me that Vision has been "replaced" with Whitney Consulting Group LLC. I think they contracted with Whitney to do the specific visitation and measure portion of the physical reassessment. So there likely is no "plot" to get a new assessor to boost values.
If you have been reassessed, validate the details carefully for accuracy. Check how much the TOWN valuation increased. If your property increased by 15% but the whole town increased 17%, you actually LOST a little value, comparatively. Watch for the town, county, and school budgets to be set and check for increases. Then wait for the tax rate to be set before you panic.