Recommended format for a large embedded stop motion animation on website?
Likely the best solution is take your frames into a video editor, set the still pix time to about 0.23 sec for each shot as you indicated you wanted to show 150 frames in 35 seconds.
35 / 150 = 0.233333333

Set your project properties to 720p, (720 x 1280 progressive)
As you have 2:1 aspect ratio there will be some letter boxing.

Or a better match maybe to use iFrame format:
960 horizontal by 540 vertical pixels assuming you are using iMovie of FCP.

Assuming iMovie, render to .mov and follow these instructions to make it a .swf movie:
http://www.ehow.com/how_8245141_export-imovie-swf.html