block id pool blocktime
691877 AntPool 00:01:15
692142 AntPool 00:15:49
692222 ViaBTC 00:07:40
Except for the first one, the other two had a normal blocktime. And 1 minute is more than enough to add transactions from the mempool into a block.
I think some pools might want to mine empty blocks to try to make fees goes higher, so they will make more money in medium term (this is my guess only, but I think it makes sense)
They aren't. You're looking at the timestamp only. The timestamp of a block is almost always inaccurate because the network allows it to deviate significantly. The blocks that you've highlighted are relayed only a few seconds apart.
Miners won't try to artificially inflate fees. Trying to inflate the fees at the current stage won't work, none of the pools hold a significant portion of the network. Intentionally mining empty blocks would result them in losing out more fees in the long run. Fees are fairly demand inelastic right now, so people are more likely to put off making transactions when fees are high.