You're misunderstanding interlacing. Interlacing was a way to still keep 50Hz (or 60Hz in some parts of the world) while having twice as many rows. It didn't give you a higher refresh rate than that.
No, but the difference in scanning pattern does provide a quite stark perceptual difference between 15KHz interlaced and 31KHz progressive at 60Hz. The scanning of fields seems to provide a higher chance that field 1's bottom lines won't have disappeared by the time the monitor is scanning field 2's bottom lines. Of course, it's largely dependent on a monitor's specific phosphor persistence, and why high-persistence monitors were so common in the earlier days of personal computing.
