Example:
I just realize why you hate me
Learn English – use realize with “just” in the present tense
adverbspresent-tense
Related Solutions
I would have been able to comment had this still been in EL&U , where it should have remained because it's an interesting grammatical question, so you'll have to settle for a short answer.
Although "what have you been doing" may have a form whose name includes "perfect", the statement doesn't have a perfective aspect - because the questioner hasn't decided the person has finished doing whatever it was.
Wikipedia says
Perfective aspect is used in referring to an event conceived as bounded and unitary, without reference to any flow of time during ("I helped him"). Imperfective aspect is used for situations conceived as existing continuously or repetitively as time flows ("I was helping him"; "I used to help people").
Had the questioner concluded the activity was over, they would have used the perfective "What have you done?" Also be aware a statement like this can imply something bad was done, so the questioner might back off from the perfective to avoid sounding rude.
Some languages (e.g Polish) have completely different verbs to express perfective or imperfective aspect; in English we settle for progressive/continuous tone.
Use "since" in its meaning of "starting in the past" with the present perfect form of the verb (have + past participle) or the present perfect continuous (have / has been + "ing" form of the verb). Your example would use the present perfect tense.
Of the three examples you give, #3 is correct for its use of "since". Your involvement began in 2015, and is ongoing.
(Incidentally, we would say "the telecom industry..." and we would not capitalize "Telecom Industry" as it is a generic term. We would only capitalize proper names, i.e. if that were the actual name of a specific company.
So correct would be: We have been involved in the telecom industry since 2015.)
Your other examples:
The first example is not idiomatic, although the meaning would be understood. "Since" does not correctly go with the simple present tense, for the reason given above. To rework this sentence, you could say, "We are involved in the telecom industry, and have been since 2015." It's a bit redundant, but it works.
The second example is not grammatically correct at all - If I were editing this, I would simply understand that the writer had omitted "been" by mistake.
Hope this helps.
Best Answer
You can, but not in that way.
If you wanted to say that you've come to know only a brief moment ago that the person you're talking to hates you, then the simplest way to change your original sentence to be correct is like this:
However, you can use the phrase "just realize," as illustrated by the reply from the other person:
Alternate version of the same question in past tense:
I don't think you can use "just realize" outside of a question, though. Someone correct me if I am wrong on this.
It should be noted that despite the fact that the tenses are different, the meanings are virtually identical. The reason is the use of the word "just," which is used as an adverb to mean that it happened very recently. We understand that the realization happened only a second ago in both sentences even though the tenses are different.