Shooting 150' from what I assume is a second story balcony isn't going to change much at all and I would not factor it in. I wouldn't even worry about being four stories up to be honest. If shooting a tiny bulls eye with a more accurate gun at four stories maybe, but a spinner target from one story no way. Plus the gun is not accurate enough to worry about that anyway.
Imo Legionnaire was the closest to correct, it's more about the pellet drop from the rifle and pellet choice than that small angle. I will add that in addition to what he said I would find the trajectory of the pellet and sight the gun to best match that, then figure out pellet drop from there for longer shots. I always sight the gun to match the trajectory, any way else is a mistake. Basically the pellet drops first thing out the barrel, and the further it goes the further it falls. The sights however have no trajectory, just a straight line like a laser. The barrel is below the sights so the deal is to make the barrel point up so it can reach the line of the sight, but the pellet will curve up to meet that line then drop so it's only on target for a very short distance. Lets say for example the pellets zenith is at 100' and you sight it to that, the pellet will be low before and after 100'. What you should do is make it so the pellet passes above that line a slight, eg 1/4". This way the pellet is at or above the line of sight for a much greater amount of time/distance. Eg it hits line of sight at 80', goes 1/4" high at 100, then on sight again at 120'. If you include 1/4" below the line of sight then the window of the pellet being within 1/4" of the sight is even greater. Eg 60' it's 1/4 below and climbing, and 140' it's 1/4 low and falling. This window of 1/4 above and below would be considered a 1/2" window or kill zone. So if the target is a tiny 1/2" spinner then you know that within 60 to 140' you'll hit it, assuming the you and the gun do your parts. If shooting birds or gophers for example the 1/2 zone is fine. Outside that window of 60-140' you will need to estimate holdover to stay on target, closer is easier, further is harder to do and the further the target the much further the holdover. So 160' might need 1" holdover, but 200' might be 5".
The problem with sighting a gun without taking the pellets trajectory and sight height into consideration could be this common mistake: Someone sights the gun at say 33' which is the standard airgun target range, and using a scope with typical tall rings. It's dead on at 33', then they try hit a bird at 100'. They assume that since it's further away they need to aim higher, but the problem is it was sighted before the pellet reached its zenith so it was actually still climbing until beyond 100', plus their holdover and the pellet sails well over the target. This is why you need to find out what the trajectory of the pellet you are using is in your gun and match the sight to that trajectory along with whatever kill zone you consider acceptable. If shooting flies then obviously kill zone I used as an example is unsat and you'll want a smaller window of maybe 1/16", just know that window will only be good over a much shorter distance, say 90 to 110'. If your gun is weaker and/or the pellet BC is lower then the zenith will be at a closer range and the window shorter. The height of your sight over the bore is also a big factor, the higher the sight the narrower the window but further out that window will be. So ideally you want the sight as low as possible, the gun as powerful as possible, and the pellet with the best speed and BC possible. Get the free program "Chairgun" and it will give you an idea of this trajectory and sight relationship. It will also tell you how your gun shoots different pellets and how sight height changes things. You can even program in the kill zone to see when the pellet enters and exits it, and better understand how much holdover you need at ranges outside your window. The only real trick to using the program is knowing the BC and velocity of the pellet from your gun which is not easy without a chronograph. If you don't know the numbers you can estimate to at least get close. Those range numbers I gave were just examples for easy understanding, don't use them to estimate your gun.
So run the program, look at the trajectory at various ranges, then change scope/sight height to understand the difference. Then change BC and velocity to those changes. It even has a function to see how shooting from your balcony affects the shot. Have fun!
