While I completely get where you're coming from, realistically this can be very messy. You'd quickly find that an increasing number of your support calls were from those users having issues. 15% doesn't sound like a lot, but 15% of a million people is 150,000 people.
So, you'd succeed in angering a lot of customers. Much better to try and inform all of your customers (not just corporate) of the upcoming changes, and provide support materials for them to follow while giving them a reasonable timeframe to do so.
Maybe you should use conversion metrics combined with usage statistics weighted against trending and flow relative to feature enhancements and capabilities instead of any raw value against general hits?
Each business is different, and even then different areas of a product can have differing requirements and needs. What is 15% for you, may be <2% and declining for others. My current and former positions see iPad users in greater numbers than any other single platform/browser, as an example. It may be better served to create features that work for the larger audience and other platforms easily supported than grasping at a fraying edge.
So, you'd succeed in angering a lot of customers. Much better to try and inform all of your customers (not just corporate) of the upcoming changes, and provide support materials for them to follow while giving them a reasonable timeframe to do so.