Question about kettlebell intervals

I'm doing a kettlebell program designed for fat loss. Basically, it's three 45-minute workouts per week. The first 35 minutes are lifts like Turkish get-ups, C&P, goblet squats, reverse lunges, etc. The last 10 minutes are conditioning. The current phase of the program involves two-handed swing intervals for the conditioning part. Last week, I did 20 seconds on/40 seconds off, averaging 14 to 15 swings per set with a 16 kg bell. This week, the intervals are 30/30, and next week, they're 40/20.

But I'm having a lot more trouble holding on to the bell this time. It's not so much a cardiovascular issue as a grip issue. I have very small hands, and by the end of the 6th round, it's stressing the hell out of my wrists and fingers. I only have one more session of 30 second intervals, so I'll deal with that the best I can. But what would be the better option for handling 40 seconds?

1. Make the rest intervals longer, e.g. 40/30 or 40/40
2. Keep the rest intervals the same but use a 12 kg bell (lighter but also has a significantly smaller handle)

I know I lose some effectiveness either way, but I don't want to just quit after 6 or 7 rounds, and I'd prefer not to put a hole in my wall because I can't hold on. So would I lose more by dropping the weight or taking longer rest periods?