I don't know what Spinervals has you doing, but the high spin recovery rides I do have me riding in zone 2 at whatever max rpm I can sustain. I start with 15 minutes of HS in a 45 minute ride and work up 45 minutes of HS in a 1.5 hr. ride. The remainder is zone 1. I try to do the spin part continuously, without stopping, so I drink or whatever before the interval. I usually run about 116-117 rpm. Low gear, like 42X23. If you go over zone 2, it's not a recovery ride. This is on rollers. Out on the road, I can pull at 135 for a while and have managed a max of 165. It's easier on the road or track.

Keep your feet flat - don't ankle. Keep a cushion of air between the bottom of your feet and the sole of your shoe - that feeling, anyway. It just takes time. This is a recovery ride, BTW. Your legs have to get used to it.

But don't worry about some max rpm. Try to get relaxed and easy at the sub-120 stuff. It's all about efficiency - neuro-muscular coordination, as they say.