wifi connection gets slow on debian 9
 

I have a dell inspiron 15 7537 running on debian 9 for over a year or so. Never had a problem with wifi, but in the last weeks it gets tremendously slow. I first thought it might be the router, but other devices connected to it work perfectly. I also tried unloading/re-loading the wifi kernel module and it didn't work. If I restart the laptop *sometimes* the problem goes away for a day or two. I noticed however that if I use a wired connection to the router and disable the wifi I get the right speed. Also, what seems to me more confusing, when I turn back into wifi I get again the right speed, this only after being connected through the wire. I'm running on a generic 4.9.0-9-amd64 kernel and the NetworkManager Applet v. 1.4.4. Here's what I get from lspci

02:00.0 Network controller: Intel Corporation Wireless 7260 (rev 73)
Subsystem: Intel Corporation Wireless-N 7260
Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 0, Cache Line Size: 64 bytes
Interrupt: pin A routed to IRQ 45
Region 0: Memory at d0500000 (64-bit, non-prefetchable) [size=8K]
Capabilities: <access denied>
Kernel driver in use: iwlwifi
Kernel modules: iwlwifi

Any thoughts on this?

the usual questions:
1. did you check logs
2. how do you know it is slow?
3. what's happened before (did you change/install/configure anything)?