My 152's burn 23lph at 2300rpm which gives 98kts indicated airspeed. Leaned out which we do above 2500ft they burn 19lph.
We have a fuel scan 450 fuel computer installed in both planes correctly calibrated. The data is bang on and is born out by the fuel used which we record when we refill.
It is possible to get 16lph at altitude corrctly leaned but you are only flying at about 78kts. The maximum they burn is 33lph which is full chat in the climb.
If I fly ours at 105kts the fuel burn is 26lph.
I have put more than 700hrs on my particular aircraft since I had the fuelscan fittted and have never seen these figures vary.
It is worth noting that the condition of the engine and the prop will will vary this figures of you are flying constant airpspeed but if flying constant RPM then they change very little.