Can I always use present perfect for all past actions instead of memorizing verb conjugations in the simple past? For example:
"Yo les he dicho, les he hecho, les he traido" ( present perfect) instead of using
"les dije, les traje, les hice" (past simple)
I want to simplify my speaking, increase my speaking speed instead of mumbling trying to remember all those conjugations.
This question would ideally be answered by someone with a working knowledge of language teaching, based on studies about best practices. I haven't been able to find something like that, so I'll just give you my opinion.
You ask if you can always use "present perfect" (that is, the tense called pretérito perfecto) instead of the "simple past" (that is, the pretérito indefinido). That would be wrong and, for most Spanish hearers, it would sound weird. Not so much in Spain, where the compound preterite is far more common, but surely in Latin America. That's a fact: the two tenses serve different purposes.
Now, if this is just a temporary approach, and it helps you build up your confidence while speaking, then I'd be all for it. The key is: does it actually help you? Will you then find it easy to switch to the correct verb forms? That is up to you. You need to be aware of what you're doing and, in time, start incorporating those irregular verbs into your speech (maybe not all at the same time). Otherwise you'll just become fluent in Weird Spanish.
Personal anecdote: I'm learning German. As in Spanish, each verb is conjugated for person and number, and also as in Spanish, there is a compound preterite and a simple preterite. Unlike Spanish, most German informal speech uses the compound tense. But for some common verbs (the equivalents of have, be, do, etc.) you must use the simple past when it's due. As it happens to you with Spanish, I'm now at the point where I employ the compound tense for all past actions, except for those verbs, but I don't know many of the (mostly irregular) simple preterite forms yet. I know I'll have to learn them some day.
So I'd say: speak as you can, for now, but don't put off learning the correct verb forms. Start with just a few of the common verbs (decir, hacer), incorporate them into your speech, and keep at them until they come naturally. Then incorporate some more verbs, and so on. They're not so many and you can use them in fixed phrases. For example, it's not that difficult to remember to start a bit of reported speech with Yo dije or Él dijo. After a while it should just come out automatically.
Yes, you may do this in your conversations. I'm glad to hear you want to prioritize fluency at this stage.
I see this as analogous to "invented spelling," a modern pedagogical concept in education of five and six-year-olds.
In your writing practice work, I'd encourage you to continue to work with both.
As you progress with your studies, you will have opportunities to expand your speaking repertoire.
There are tons of great verbs that use a regular simple past tense. As an intermediate step, you may want to build up a bank of go-to regular past tenses to draw on.
Small comment about your object pronouns:
Yo he les dicho, les hecho, les traido
You're going to want to put "les" in a different spot:
Yo les he dicho.
Sometimes you'll want to use a different object pronoun, "los" instead of "les". For example, if you want to say that you made the two cakes already, then it would be
Los he hecho.
(Note that I omitted the subject. Fun thing you can get away with in Spanish!)
Explicitly and actively using only the present perfect tense to convey the past is not the correct way to approach speaking about the past. This technique you're describing is more of an anti-technique than anything else.
What if you wanted to tell someone that you ate yesterday? Or what if you wanted to tell someone that you were eating when something occurred?
You can't just say
I have eaten when the parade started.
We have spoken when the teacher asked the question.
You have told the students last week about the test today.
In the above examples, the use of present perfect is not correct. Although those examples are not in Spanish, they would sound just as confusing if translated into Spanish. In these examples, you would use pluperfect (past perfect) instead.
--
Yo habia comido cuando comenzó el desfile.
I had eaten when the parade started.
--
Habíamos hablado cuando el maestro preguntó la pregunta.
We had spoken when the teacher asked the question
--
Les habías dicho a los alumnos la semana pasada del examen hoy.
You had told the students last week about the test today.
But, your question asked about using present perfect for all instances of the past. So those examples would read a lot differently.
Look back at the very first example, it has more to it than just "I have eaten". It also says that the parade started (a past tense). That part isn't being conjugated as present perfect, so to be consistent, you'd end up with something like this if you substituted present perfect for all forms of the past.
He comido cuando el desfile ha comenzado.
I have eaten when the parade has started.
At this point, it should definitely feel like you are cutting corners as a speaker when saying things this way. This would confuse listeners more than it would convey your actual thoughts and emotions. It takes just as much effort to learn something correctly than it does to learn and practice it incorrectly, so you're better off doing it the correct way. You're only hurting yourself by practicing bad habits.
And here, I leave my concluding statement,
I have answered your question
People would understand you, but it would be weird.
In general, being lazy is usually a recipe for disaster. (It's exaggerated in this case, of course). I think you should try to do things well instead of making them "short" or "easy".
I think you're focusing it wrong: you don't have to learn all the conjugations alone and then recall each one of them. It's like learning the pieces and then builting up every sentence. That's truly slow and artificial.
Instead, you should read and practise things altogether wit context. You will actually learn those conjugations, but it will be more unconciously. You have to use them in context, so that everytime you're about to say "tu fue" sounds bad to you for some reason, and the only one that sound good to you is "tu fuiste".
