I think it is not correct to state that crossing isobars only matters to jets. I fly in the alps and if there is Foehn (the Chinook of the Alps) then there are pressure differences in excess of 15 hpa between North and South of the mountains. This can become relevant. There is the problem of «from high to low watch out below», but also the wind and resulting downdrafts easily exceed the airplanes capability to climb.
This is indeed relevant to you and your C150.
Also, without mountains in the equiation, it is possible that air pressure drops at extreme rates during a couple of hours.