Carrying a 40kg backpack, as suggested by one commenter, is not a good analogy. The backpack does not account for the differences in blood pressure, and there are other important differences that we will get to shortly. But let's first consider the blood pressure issue!
A great body (no pun intended) of knowledge about the effects of excess $g$-forces on the human body comes from military research that tries to determine what the limits are for fighter pilots (who necessarily experience high acceleration when they pull tight turns).
High-G training for pilots of high performance aircraft or spacecraft often includes ground training for G-LOC in special centrifuges, with some profiles exposing pilots to 9$g$ for a sustained period.
Of course, this requires a $g$-suit and a lot of training on top of starting with a genetic background that permits a level of physical fitness that is not particularly representative of the capabilities of the average human being. Also, the pilots are sitting, not standing.
Fortunately, the air force also ran a few experiments on untrained people for comparison:
An un-trained individual not used to the G-straining manoeuvre can black out between 4 and 6 g, particularly if this is pulled suddenly.
So, we can safely conclude that 1.5$g$ is definitely not a blackout condition for the average Joe, even in a standing position. The difference between sitting and standing is only a slight one, because sitting does not prevent the blood from rushing from your knees to your feet. It only prevents the pressure differential over the length of your thigh (which is on average about 1/4 of a person's height).
In terms of effort expended to stand and more around, yeah, at 1.5$g$ you will feel 1.5 times your body weight. However, this is not equivalent to carrying a 40kg backpack for an 80kg person because the additional weight is very optimally loaded - it's configured precisely like the load you normally carry around, just 50% higher everywhere in your body. Whereas a backpack will produce a lot of non-uniform loading and be much more cumbersome for the same effective increase in weight.
The limiting factor at 1.5$g$ will probably be the blood oxygen flow to the upper back and neck muscles, needed for maintaining a standing pose. The reduced blood flow, coupled with the increased weight demand at 1.5$g$ would likely prevent the muscles from operating aerobically. Thus, rather than burning oxygen, the muscles would have to generate energy through glycolysis as they do during in an intensive workout. This will result in operating normally for a while but eventually reaching a state of fatigue, probably within 30 minutes or so for the average Joe but likely extendable to a few hours for a physically fit person with training in such an environment.
The fix for our hero, obviously, is to lie down when he is tired and allow his/her back and neck muscles to recuperate under conditions of normal blood flow. If some loss of dignity is acceptable, our hero may also resort to crawling around on all fours and minimizing the amount of time spent standing (since standing causes the bulk of the endurance penalty in our 1.5$g$ environment).
Our hero should also use every opportunity to swim from point A to point B, because being submersed is like wearing an ideal $g$-suit - the pressure differential is approximately the same outside the body as in and blood flow will be close to normal so there would be no endurance penalty for additional $g$s. If our hero gets tired while swimming he or she should definitely not attempt to tread water though - the higher $g$ value will amplify the water pressure, making it much more difficult to breathe since our neat argument of equal submersion pressure doesn't apply the interior of the lungs which are at only air density rather than approximately water density. Instead, our hero should just lie back and relax while floating near the water's surface.