Checkout Known Upgrade Issues When Upgrading To Microsoft Dynamics GP 2015 R2 from the GP Support Team
Known Upgrade Issues When Upgrading To Microsoft Dynamics GP 2015 R2 – Microsoft Dynamics GP Community
Install, Upgrade & AdminMicrosoft & the GP EcosystemGP 2015
Archived post from 2015. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.