Happens in 0.73.107769 for me too.

Don't only look at your FPS when claiming bad performance. My fps does drop about 20 fps when having two smokes and exploded car but my GPU usage was 99% already when there was no smoke. Please, check your GPU usage on same scenario. If it is over 90% already when there is no smokes then you can except fps drops when throwing smokes. GPU can't magically have more performance when there is even more GPU heavy stuff on screen.

Fixed in development branch version: 0.73.107682