30 secs - that's all a superspin is. Learning to produce short bursts of speed with a fast stroke is beneficial. If you're bouncing off the saddle, you need to slow the cadence, practice a smooth stroke until you can get your cadence up fairly high for a short period of time. You don't have to hit the same high as anyone else but a superspin will show you where your stroke breaks down. Everyone has an optimum cadence for their body, but 90 is slow in some people's book.

If a class is "mostly cadences of like 150" the instructor needs some instruction.