BigBlueButton how to make display sharing more responsive, or tell me another tool?

Question

BigBlueButton

Good afternoon. For webinars I want to use bbb. In principle, everything suits, except for the insanely slow display sharing (for me this is significant). Moreover, the demos from the site are similar. From the docks / Google could not find anything. Those. as I understand it, it takes periodic pictures and sends only when the picture changes. But apparently these pictures are very periodic. I would prefer to make him drive the flow. In general, if anyone knows how to solve the problem - please respond. Or suggest another product. Requirements:
1. The ability to fumble the display (not bad, if possible, the area, but not critical) - understandable without brakes
2. showing presentations
3. completely free. at first we have about 30 users, but the number can grow
4. it doesn't matter your server (there is where to host) or an external resource. The main thing is to be able to hold a webinar at any time
5. the ability to drive sound through the same system
6. a drawing board is desirable