I spent considerable effort and time fixing sprite loading lag. But I didn't succeed.
I've pursued and tried every potential method listed in the ActionScript 2 Language Reference manual, searched internet but no result. There is no way in Flash AS2 to load object from file before it's placed on the stage. There is also no way to move or copy object across flash timelines so there is no workaround in placing all sprites behind the scene on zone load and moving them on/off stage as player viewpoint changes. At least not synchronously with viewpoint move.
I can thing of workaround in placing/loading all viewpoints with sprites at once on file load and then moving entire viewpoint on/off visible area instead of placing/creating and then removing them. But that involves substantial change in how HTH game works = awfully lot of work.
**** this, lets live with lagging sprites.