wp_options table is over 500mb?!

Hi, I’m having a real big issue with my site. It’s very slow, especially in the backend which I of course think is related to the huge wp_options table. I’ll admit, I have a couple of plugins, but all of them are important, ranging from WooCommerce to User Role Editor, BridgeDD with phpbb forum (which is instantly fast btw, so it’s not that)…

I’ve read up on Google that so called “transients” seemed to be the culprit as to why the table get’s so huge. However, I downloaded a plugin that removed all of them (there were only like 4000 rows, which was around 4kb in size) so that didn’t help at all. Now I’m kinda stumped. What should I do? I’ve almost tried every database optimizer tool in existence and nothing is helping me. :/