Yeah, it's probably okay to use the world's most common primary training aircraft for training. Aside from people's personal weights seeming to increase in more recent times, nothing else has changed from the inception of the 150 to make it any less ideal as a trainer. Like all aircraft, the 150/152 must be maintained properly, and flown within their limitations. As said, few aircraft can fly within limits with full tanks, and full fuel. Even the Cessna 310 I used to fly fell into this category.
My opinion is that the 150/152 are weight limited because of performance, not structure. I hold this opinion because both can have gross weight increase with no structural change, but an increase in power.
Therefore, it would be very unwise to fly these aircraft overweight. Think of it as an excellent incentive to keep one's weight "normal". Perhaps the 170 pounds per person of the design criteria might be a bit optimistic, but when two of you and full fuel won't work anymore, there may be a message in there for the occupants.