switch from rhel6 to rhel7 , system become slow, perhaps memory issue

Since I have switch form rhel 6 to rhel 7 , all system become slow.

My workstation is a bi xeon, 24 cores (12 hyperthreaded), with 78.4GiB of RAM.

I suspect first the memory because I launch a lot of applications and still when I launch free -m :

[bgy@localhost cmake-build-debug]$ free -m
              total        used        free      shared  buff/cache   available
Mem:          80320        8083       55796         254       16440       70939
Swap:          4095           5        4090

only 8083 is used.

I make a small program , just to view the limit of allocated / usable memory

#include 

void main()
{
    int* array = (int*)malloc(4L*15L*1000L*1000L*1000L);
    std::cout  "Hello world!"  std::endl;

    for(long long i = 0 ; i  15L*1000L*1000L*1000L; i++) {
        array[i] = 1;
    }
    std::cout  array  std::endl;

    //delete[] array;
}

I could address all the memory , but the speed is really slow (1GB/ second) compared to the theorical bandwith (40GB/s).

I am in dual boot with windows , and it does not have such issue. So I suspect it come from the soft.

I also check the susbcription manager and my suscription is valid until 2020.

I do not know what test to do next.