What's the time complexity of this algorithm.Can i make it faster?

this algorithm finds the most overlapping activities(bands) in specific intervals that start at arrl and ending at depr.I used quicksort for O(nlogn) time complexity and then a while loop with O(n) to count the number of conflicting activities at these intervals 1.So is this like O(nlogn) + O(n) time complexity? 2.Can i make it even faster at O(n)? 3.Lastly,theoretically,is it possible to use Timsort for O(n) time complexity?

Code written in C is for 15 activities,but let's say it's generalized and with unsorted arrl and depr

EDIT:The result is the most activities at a 1 hour period

void findMaxBands(int n,int arr1[n],int depr[n]);
void quickSort(int a[],int l,int h);
int partition(int a[],int l,int h);

int main(){
    int arrl[15] = {18,18,19,19,19,19,20,20,20,20,21,22,22,22,23};
    int depr[15] = {19,21,20,21,22,23,21,22,22,23,23,23,24,24,24};
    int n = 15;
    findMaxBands(n,arrl,depr);
    return 0;
}

void findMaxBands(int n,int arrl[n],int depr[n]){
    quickSort(arrl,0,15);
    quickSort(depr,0,15);

    int guestsIn = 1,maxGuests = 1,time = arrl[0];
    int i = 1, j = 0;

    while (i < n && j < n){
        if (arrl[i] <= depr[j]){
            guestsIn++;
            if (guestsIn > maxGuests){
                maxGuests = guestsIn;
                time = arrl[i];
            }
            i++;
        }
        else{
            guestsIn--;
            j++;
        }
    }
    printf("Maximum Number of Bands : %d at time %d-%d",maxGuests,time-1,time);
}

void quickSort(int a[],int l,int h){
    int j;
    if(l<h){
        j=partition(a,l,h);
        quickSort(a,l,j-1);
        quickSort(a,j+1,h);
    }
}

int partition(int a[],int l,int h){
    int v,i,j,temp;
    v=a[l];
    i=l;
    j=h+1;

    do{
        do{
            i++;
        }while(a[i]<v&&i<=h);
        do{
            j--;
        }while(v<a[j]);
        if(i<j){
            temp=a[i];
            a[i]=a[j];
            a[j]=temp;
        }
    }while(i<j);
    a[l]=a[j];
    a[j]=v;
    return(j);
}

1.So is this like O(nlogn) + O(n) time complexity?

O(n log(n)) + O(n) = O(n log(n))

Ref. eg. Big O when adding together different routines for more details.

2.Can i make it even faster at O(n)?

3.Lastly,theortically,is it possible to use Timsort for O(n) time complexity?

A general purpose (comparison) sort algorithm might have a best case complexity of O(n), but the average/worst case would have a complexity of O(n log(n)) at best. You can find an overview of several sort algorithms here with their complexities.