This is expected, your chipset is not part of the family that received the speed improvements recently. I had a similar one on my laptop and I replaced it with https://www.amazon.it/dp/B0B39631G1I'm getting the same snail speed 16Mbps
iwm0@pci0:2:0:0: class=0x028000 rev=0x73 hdr=0x00 vendor=0x8086 device=0x08b1 subvendor=0x8086 subdevice=0x4060
vendor = 'Intel Corporation'
device = 'Wireless 7260'
class = network