At the time of writing the average fees for this month has been 0.27BTC per block (266BTC for 964 blocks), that's 4.4% of the block reward (6.25BTC), so even if the mempool was completely empty 15% drop in the hashrate is not possible.
Fees were quite heavy and you can see surplus hr adjust at time. Average fee when I post was about 0.6 BTC for a a couple hours, easily correlate profit switchers adjusting to it. Which fee are still up on 24 rolling average close to a 6.6 reward.