Insulated tiles shouldn't be heating up your farms quickly. That's the point of insulated material: the thermal conductivity is so miserably low that it hardly transmits heat at all. It's possible that the heating came from the rock that you mined to create the farm. Items dropped on the ground don't transmit heat to surrounding tiles, but they do transmit heat to the air/liquid on that tile. Since your farm heated up quickly and you had a hard time cooling it, it's likely that you had to not only cool the air inside your farm, but also the tons of mined rock inside your farm. Your screenshot doesn't show any debris right now, so your farm should easily stay cool using your existing Wheezeworts.
There are a few other possible sources of heat I can see in the screenshot:
- The ceiling of your farm isn't insulated, though it seems cool.
- The bottom of the screenshot seems warm. Is there insulation underneath your farm, or possibly another heat source?
- There's a water pipe going through your farm. It doesn't seem warm, but keep in mind that water pipes do transfer heat to their surroundings. (Insulated pipes will transfer much less heat.)
A personal example: I decided to water-cool some Mining Lasers that were in vacuum. The floor was littered with meteorites that were 300C, and so the water I pumped in flash-boiled as it tried to cool the tons and tons of meteorites. The Mining Lasers weren't getting heated by the meteorites before I added the water, but after I added the water, they absorbed heat from the steam in the tile. (I fixed the problem by deconstructing and then re-building the floor tiles, so that the debris fell down onto my solar panels. Solar panels break at a mere 75C, but since they were in vacuum, the debris didn't transfer any heat to the air, and thus nothing transferred heat to my solar panels.)