Пожалуйста, напомни мне, что пятнадцатого июня у нас встреча, а не двадцатого мая.

Напомни is the imperative form of напомнить, which means to remind.

A few important points:

• напомнить is perfective
• the imperative напомни means remind me / please remind me
• perfective is natural here because the speaker wants one completed reminder, not an ongoing process

Compare:

• напомни = remind me (once, successfully)
• напоминай = keep reminding me / remind me repeatedly

So in this sentence, напомни is exactly the normal choice.

Because the verb напомнить usually takes the person being reminded in the dative case.

So:

• напомни мне = remind me
• напомни ему = remind him
• напомни нам = remind us

This is different from English, where me does not visibly change form. In Russian, the grammar requires dative here.

A useful pattern is:

• напомнить кому что
• literally: to remind someone of something

In this sentence:

• мне = to me
• что... = what I should be reminded of

Here что means that and introduces the content of the reminder.

So the structure is:

• напомни мне, что... = remind me that...

This is very common in Russian:

• Я знаю, что... = I know that...
• Он сказал, что... = He said that...
• Напомни мне, что... = Remind me that...

So что is not what here. It is a conjunction meaning that.

Because Russian dates are often expressed with:

• the day in the genitive
• the month also in the genitive

So:

• пятнадцатое июня would be wrong
• пятнадцатого июня = on the fifteenth of June
• двадцатого мая = on the twentieth of May

This is the normal way to state a calendar date after an implied on.

Examples:

• первого января = on the first of January
• десятого марта = on the tenth of March
• двадцать пятого декабря = on the twenty-fifth of December

Yes, you can think of числа as being understood.

Historically and grammatically, expressions like:

• пятнадцатого июня

can be understood as something like:

• пятнадцатого числа июня

But in normal modern Russian, числа is usually omitted.

So learners often benefit from thinking of the pattern this way:

• какого числа? = on what date?
• пятнадцатого = on the fifteenth

That helps explain why the ordinal number appears in the genitive.

Because у нас встреча is the natural Russian way to say we have a meeting.

Literally, it is closer to:

• at us there is a meeting

But in real usage it means:

• we have a meeting
• there is a meeting for us / on our schedule

This у + genitive structure is extremely common in Russian for expressing possession, availability, or scheduled events.

Examples:

• У меня есть машина. = I have a car.
• У нас урок. = We have a lesson.
• У них собрание. = They have a meeting.

So у нас встреча is idiomatic Russian.

Because а is often used when contrasting one thing with another, especially when correcting or replacing one option with the right one.

So:

• ...встреча, а не двадцатого мая = ...the meeting is on the fifteenth of June, not the twentieth of May

Here а не has the sense of:

• and not
• rather than
• not X but Y

Compare the feeling:

• но = but, often showing contradiction or obstacle
• а = and/but, often showing contrast between two alternatives

In this sentence, the speaker is correcting the date, so а не is the better choice.

Russian often states dates without a preposition when the date itself already functions adverbially.

So:

• встреча пятнадцатого июня = the meeting is on the fifteenth of June
• я приеду десятого мая = I’ll arrive on the tenth of May

This is a normal pattern.

You can sometimes see prepositions in other date expressions, but in straightforward calendar dates, Russian often just uses the genitive date form by itself.

So the sentence does not need в before пятнадцатого июня.

Russian punctuation requires a comma before что when it introduces a subordinate clause.

So:

• напомни мне, что...

needs a comma, just like English often does with a clause boundary.

There is also a comma before а не because it connects contrasting parts of the sentence:

• ..., а не ...

So the commas reflect the sentence structure:

1. main clause: Пожалуйста, напомни мне
2. subordinate clause: что пятнадцатого июня у нас встреча
3. contrast: а не двадцатого мая

Yes. Russian word order is flexible, but changing it changes the emphasis.

The original:

• Пожалуйста, напомни мне, что пятнадцатого июня у нас встреча, а не двадцатого мая.

sounds natural and neutral.

Possible variations:

• Пожалуйста, напомни мне, что у нас встреча пятнадцатого июня, а не двадцатого мая.
• Пожалуйста, напомни мне, что у нас встреча не двадцатого мая, а пятнадцатого июня.

These are also possible, but they highlight different parts more strongly.

In Russian, the end of the sentence often carries important or contrastive information, so word order helps manage emphasis.

Пожалуйста here means please.

It makes the imperative more polite:

• Напомни мне... = Remind me...
• Пожалуйста, напомни мне... = Please remind me...

It can appear in different places:

• Пожалуйста, напомни мне...
• Напомни мне, пожалуйста...

Both are natural. The second version is also very common in everyday speech.

So пожалуйста is flexible in position, but its function is simply to soften the request.