You need to have it jumped if you move the distributor, so that it doesn't try to compensate for your changes. If you are just checking the timing, all that is required is the normal warm idle. 1500rpm is obviously too high, you need to get it under 1k, whatever is "normal" for your car once completely up to temp.

However, when I first set my timing, the idle was around 1,100 (EACV probs.) and so I disconnected it (again, EACV) and it first dropped real low, around 400, then back up to a steady 900 (just going off tach.) so I set it a bit more advanced than you normally would, just a guestimate. After cleaning the EACV and resetting things, the idle was normal, around 700rpm on the tach. I checked the timing then and it was perfect (red mark lines up with pointer and the v-groove).

It should start to advance itself, at least when the service connector is not jumped, as soon as you get the rpms up, even a little.

edit: and the first time I set it, I thought it was right or close to it, but it was actually pretty much all the way at max. retard. For some reason, in the bright sunlight w/ the timing light, the white TDC mark looked like it had a slight red tinge (prob. blending in with the correct red timing mark). Maybe that's why it had been set wrong to begin with. At night, it was very clear, and you could easily see the red mark.