El movimiento del ascensor es lento.

Spanish often uses an abstract noun like movimiento (movement) to focus on a specific aspect of something.

• El ascensor es lento = the elevator itself is slow (more general).
• El movimiento del ascensor es lento = the elevator’s movement (speed/way it moves) is slow (more specific, and a bit more formal/technical).

del is the contraction of de + el:

• de el ascensor → del ascensor
  It’s mandatory in standard Spanish whenever de is followed by el (the masculine singular the). (Same idea as a + el = al.)

Because ascensor is a masculine noun in Spanish: el ascensor.
Gender is grammatical, not based on real-world “male/female.” So it takes el (and therefore del).

Adjectives agree in gender and number with the noun they describe:

• El movimiento (masculine singular) → lento (masculine singular)

Position: in Spanish, descriptive adjectives commonly go after the noun: movimiento lento. Putting it before (lento movimiento) is possible but sounds more literary/stylized and can subtly change emphasis.

Not normally. For “slow” as a characteristic, Spanish uses ser: es lento.
Estar is used more for states/conditions, but estar lento is generally unnatural in this context. You might hear:

• El ascensor está lento hoy (more colloquial, implying “it’s running slow today”)
  But the more standard/neutral phrasing is El ascensor va lento or El ascensor está yendo lento (less common).

Movimiento is correct and neutral. Alternatives depend on what you mean:

• La velocidad del ascensor es baja = the elevator’s speed is low (more technical).
• La subida del ascensor es lenta = the upward ride is slow.
• La bajada del ascensor es lenta = the downward ride is slow.
• El ascensor va lento = the elevator is going slowly (very natural).

It can cover both ideas depending on context:

• Speed: El movimiento es lento (it moves slowly).
• Taking time / progress: El proceso es lento (the process is slow / progressing slowly).
  In this elevator sentence, it mainly points to movement speed.

Not in the same structure. Lentamente is an adverb and would modify a verb, not a noun. For example:

• El ascensor se mueve lentamente. = The elevator moves slowly.
  But with ser
  • adjective, you use an adjective: es lento.

Está siendo means “is being” and usually implies a temporary or unusual behavior, often with a nuance like “it’s being slow (right now / for some reason).” It’s possible but marked:

• El ascensor está siendo lento hoy. = It’s being slow today (maybe due to a problem).
  For a neutral description, es lento is preferred.

If both noun phrases become plural:

• Los movimientos de los ascensores son lentos. = The movements of the elevators are slow.

If only the elevators are plural but you still mean “the movement (in general)”:

• El movimiento de los ascensores es lento. (singular movimiento, plural ascensores)

Everything must agree: el/los, es/son, lento/lentos.

Yes, it sounds a bit formal/technical because of El movimiento del ascensor. In everyday conversation, people often say:

• El ascensor va lento.
• El ascensor está muy lento. (common in speech)
  But the given sentence is perfectly correct and clear.