Since the Earth is supposedly millions of years old, where is the evidence of the "Ordovician," and "Permian," and "Carboniferous" mountain ranges? Hundreds of millions of years of supposed slow mountain uplift?
You say in 15 million years the Himalaya mountains will be miles higher, so where are the ancient mountain ranges which must have risen over hundreds of millions of years?
The localized uplift of the Himalayas, and I think the Andes, and maybe others, is residual movement from the runaway tectonics of the Deluge, just a local phenomenon.
Just look up the sediment load and flow of all the major rivers, factor in the small rivers, and you'll discover the rough calculation that the continents, at current erosion rates, should have leveled to sea level within 15 million years.