[sammyg2]

Playing with the a/f mixture is something that you need to be very careful with. A very small turn of that screw makes a large difference and it's easy to get it way out of adjustment.
It is normal for the idle to climb a little when it is richened up, but maybe not as much as you described.

The idle speed adjustment screw isn't a throttle stop, it is a bypass metering screw that lets air go around the throttle plate.
If you have it screwed all the way in and the idle is still too high, check your throttle linkage to make sure it isn't holding the plate open.
If the throttle plate is against the stops isn't held open by the linkage, and the screw is turned in all the way and the idle is still at 1500, I'd say you have a large vacuum leak.