Don't give up.
Expand your search from 75000000000000000 to 75FFFFFFFFFFFFFFF.
It's only 1152921504606846975 keys to check. With 8 x RTX4090, assuming 36 billion keys per second and running 24/7, it will only take about 370 days.
And you can cut that time down to just under 3 days with 1024 x RTX4090's. 
Be a team player - do it and please report to us what you find, thanks.