The beam angle you require for your LED light can be determined by what height your ceiling is from the object or floor space to be illuminated, and what lux level (brightness) is required in that particular area.
Selecting the right beam angle is important for both the look & feel of the room, & also the practicality of the working light. Usually, the widest lens available is 60° & this is most commonly used for general purpose lighting. If you are looking to highlight a particular feature or object, i.e. a statue or a kitchen bench, then a more focused beam may be necessary. Wide beam angles & high ceilings can leave low overall levels of light. This is especially true if the light is being absorbed by the surrounding walls & not getting to where it is needed. The opposite is also true, as with narrow beam angles & low ceilings you will get a very uneven light, which will also produce a hot spotting effect on the floor.
If you want to check the consistency of the light, a good trick is to walk around it with a sheet of A4 paper at waist level & observe the light on the paper. If you want to know if theres enough light to work with, then use a sheet with writing on it & try to read it as you walk. If you're retrofitting, a good method of selecting your LED would be to look at the existing lighting & then decide what you like & what you'd change.
Unless you've got very high ceilings, a 60° lens is the safe bet. If you're trying to focus light over a bench with a standard 3 metre high ceiling, then 45° is probably best. If you want to spotlight a statue or similar, then try 30°. Only in a very rare circumstances should you select a 15° beam.
Note: The wider the beam, the quicker the light will lose its intensity. As there is only a fixed amount of lumens emitted from each lamp, energy is wasted if the light strays outside of the area to be illuminated.