1866(PC3 14900) vs. 1866(PC3 1500) ?????

There isn't a real difference, at least not one that matters for performance. Any difference in Newegg posting is probably just a difference between how the companies rate the modules (there can be minor discrepancy between how companies adhere to specifications in naming conventions). The difference is probably caused by some companies truncating the PC314900 number whereas some round up to PC3 15000 instead of truncating.