Arduino pro mini running extremely slow

Hey guys, I own Arduino uno r3 (original) and Arduino pro mini 5V on ATMega328 (original), and my issue is:

I’m fooling around with LCD and RTC modules on my Arduino Uno using l2c interface, everything works smoothly, time on lcd will refresh itself every second (500 miliseconds of delay in the code) but after i upload very same code on my Arduino Pro Mini it will refresh itself every 10, 15 seconds, sometimes way longer than that. No changes whatsoever were made to the sketch I’m uploading on them both, both arduinos are running on ATMega328, so why are they acting so different?

here is my code if it helps with anything:

#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>
#include <Ultrasonic.h>
#include <DS1307.h>

char date[20];
char time[20];
int RTCValues[7];

#define TRIGGER_PIN  12
#define ECHO_PIN     13
Ultrasonic ultrasonic(TRIGGER_PIN, ECHO_PIN);

#define I2C_ADDR    0x27 // <<----- Add your address here.  Find it from I2C Scanner
#define BACKLIGHT_PIN     3
#define En_pin  2
#define Rw_pin  1
#define Rs_pin  0
#define D4_pin  4
#define D5_pin  5
#define D6_pin  6
#define D7_pin  7

int n = 1;

LiquidCrystal_I2C	lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);

void setup()
{
  lcd.begin (16,2); //  <<----- My LCD was 16x2

  
// Switch on the backlight
lcd.setBacklightPin(BACKLIGHT_PIN,POSITIVE);
lcd.setBacklight(HIGH);

  DS1307.begin();


}

void loop()
{
  float cmMsec, inMsec;
  long microsec = ultrasonic.timing();

       // go to start of 2nd line
  
   DS1307.getDate(RTCValues);
   lcd.home (); // go home
    sprintf(date, "20%02d-%02d-%02d", RTCValues[0],
            RTCValues[1], RTCValues[2], RTCValues[4]);
       lcd.print(date);
           
        sprintf(time, "%02d:%02d:%02d",  RTCValues[4], RTCValues[5],
            RTCValues[6]);   
      lcd.setCursor (0,1);       
    lcd.print(time);
    lcd.print("-");
    lcd.println(fromNumberToWeekDay(RTCValues[3]));
delay(500);
    
}

Sounds like the Promini fuses were not set to use 16 MHz crystal, but instead use the internal 8 MHz oscillator with the divide by 8 clock prescaler - which is the default factory setting.

CrossRoads:
Sounds like the Promini fuses were not set to use 16 MHz crystal, but instead use the internal 8 MHz oscillator with the divide by 8 clock prescaler - which is the default factory setting.

I just researched how to change fuses and changed them to the values expected from this model, everything works excellent.

What caused them to change?

Never set to start? Something you did?